One Thing Has to Be Impossible
Two sources must never energise the same conductors. That single requirement generates most of what follows, and it is not a preference or a good habit — it is the condition under which a utility crew can work on a de-energised line without being killed by a house four streets away. Feed a running set into a dead service and the pole transformer steps it back up to primary voltage on the line side, on conductors somebody has already tested dead and is now standing on.
The hazard also runs the other way. Utility power restored onto a running alternator that is out of phase with it produces a torque impulse through the crankshaft and coupling that can shear hardware and destroy windings, and it happens in the instant the supply returns, unwitnessed, at whatever hour the outage ends.
So the arrangement has to make simultaneous connection mechanically impossible. Not procedurally impossible. A laminated instruction sheet taped inside a panel door is not an interlock, and neither is an owner who understands the sequence today and will be tired, cold and holding a torch the night it matters. Every legitimate arrangement below is a physical impediment.
Which rules out the cord with a male plug on both ends. It works, which is exactly what makes it lethal: it energises the pins on the other end, it defeats the main breaker, it puts full service current through a cord sized for a lamp, and the household that has been using one for eleven years will tell you it has never given trouble.
Three Arrangements, Ranked by What They Ask of the Owner
A mechanical interlock kit is the cheapest legitimate answer. A sliding plate mounted on the panel dead front physically prevents the main breaker and a backfeed breaker being switched on together — move one and the other is blocked. The kit has to be listed for that specific panelboard, from that manufacturer, in that position; a generic plate drilled to fit is an unlisted modification to a listed assembly and it fails inspection on sight. The whole panel stays live during an outage, so the owner manages load by switching individual breakers off and on, which demands both understanding and discipline.
A manual transfer switch is a separate enclosure carrying six, eight or ten circuits, each with its own selector and often its own meter. The circuits are chosen at installation and moving one later means rewiring. It is the arrangement that best suits a portable set and an owner who wants a short, unambiguous procedure: start the machine, plug in, throw the switches in order.
An automatic transfer switch senses loss of supply, starts the set, waits for it to reach voltage and frequency, transfers, and reverses the whole sequence when the utility returns and stays returned. It costs the most and asks nothing of anybody. It is also the only arrangement that works when the house is empty, which is precisely the outage that empties a freezer and freezes a heating system.
Choose by picturing who will be standing at that panel at three in the morning in February. An interlock kit in the hands of a competent owner is an excellent installation. The same kit in a rental property, or in a house whose occupant has changed since it was fitted, is a hazard waiting for its moment.
Which Loads Travel
The carried-load list is a negotiation, and it goes badly when it happens at the quotation stage in general terms. Sit down with the actual panel directory and mark every circuit as carried or not carried, in ink, with the owner present. The list that emerges is the specification for everything downstream — switch rating, feeder size, panel arrangement and fuel provision all follow from it.
What consistently has to travel: the heating controls and circulator, which are small loads doing the work that stops pipes bursting; the well pump; the sump pump and any sewage ejector; refrigeration; one lighting circuit per floor; the boiler or furnace ignition; a receptacle in the kitchen and one where somebody will charge a phone; and any medical equipment in the house, which outranks all of it.
What consistently does not: the electric range, the clothes dryer, the second air-conditioning system, the hot tub, the workshop, the pool pump, and the car charger. Each of these is capable of consuming a small set on its own, and their absence for a day is an inconvenience and not a loss.
Electric water heating is the argument that always happens. A resistance tank is a very large load doing something a household can genuinely go without for a day, and dropping it off the list shrinks the machine by a rating step. Where the owner refuses, a load-management module gives you the compromise: keep the whole-house transfer and let a priority controller shed the tank and the range whenever the set approaches its limit.
The carried-load argument is easier to hold with the dwelling's calculated demand on the table, because it shows the owner how much of their service the items they want to keep actually represent.
The total livable floor area of the dwelling used for general lighting load.
20A kitchen/dining small-appliance circuits, each counted at 1500 VA.
Dedicated 20A laundry branch circuits, each counted at 1500 VA.
Sum of the nameplate VA for fixed appliances such as the water heater, range, oven, and dryer.
The nominal service voltage supplying the dwelling.
Estimated required service amperage
38 A
This is a SIMPLIFIED illustrative version of the NEC 220 standard method, omitting several real-world factors (HVAC load, EV chargers, largest motor load addition, optional calculation method). Fixed appliances are carried at 100% because this page takes a VA total and not a count; 220.53 permits 75% where four or more fastened-in-place appliances are present, and a range or a dryer has its own table (220.55, 220.54) that this does not apply. It is NOT a substitute for a complete NEC Article 220 load calculation performed by a licensed electrician, which determines your actual required service size and is required for permitting. Always round up to the next standard breaker/service size (100A, 125A, 150A, 200A) and consult your electrician.
- Total connected load (before demand factor)
- 13,030 VA
- General lighting and receptacles, after the 220.42 factor
- 5,110.5 VA
- Fixed appliances, at 100%
- 4,000 VA
- Demand load
- 9,110.5 VA
They open the calculator with your figures already in it
Home Electrical Service Panel Amperage Sizing Calculator: 37.96 A — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 38 A — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Amps are not spaces. This sizes the SERVICE and says nothing about the panel's physical capacity — a dwelling can sit comfortably inside 100 A of calculated demand and still need a new panel because every breaker position is taken, the busbar is rated below what is being added to it, or the enclosure will not accept the breaker type the new circuits require. Panels get replaced for spaces at least as often as for amperage.
- The amperage is where the rest of the sizing starts, not where it ends. Service-entrance conductors, the grounding electrode conductor, the meter base, the mast or lateral and the utility's own drop or transformer all follow from this number and none of them fall out of it — and a dwelling service gets its own conductor allowance under NEC 310.12 rather than the general ampacity table, so the wire for a 200 A house is not the wire that table would give it.
- One dwelling unit. A second unit on the same service, an ADU, or a detached garage or workshop on a feeder are not added by piling their loads into these boxes: a multifamily service runs through 220.84's own demand table, and a feeder to an outbuilding is calculated as its own load under 220.40. Stacking two dwellings into this page understates both of them.
Rebuilding the Panel Around the List
Where the answer is an essential-loads subpanel, the circuits on the list get physically relocated into it, and that relocation is where the defects come from. Two-pole loads need adjacent spaces on opposite legs. Arc-fault and ground-fault breakers move with their circuits and have to be available in the new panel's product line. Anything sharing a neutral has to move as a unit.
That last one is the failure that hurts. A multiwire branch circuit puts two hot conductors on opposite legs sharing one neutral, and the neutral carries only the difference between them. Move one leg to the essential panel and leave the other behind and the two are no longer on opposite legs of a common source — the neutral now carries the sum. It will run hot indefinitely with nothing tripping, in a wall, above a ceiling, for years. Trace every shared neutral before a single circuit moves, and where the origin is uncertain, move both legs or move neither.
Count spaces honestly and then add some. An essential-loads panel sized exactly to the list has no room for the circuit the owner adds in year two, and the next contractor will solve that with a tandem breaker the enclosure may not be listed for. Two or three spare spaces cost almost nothing at order stage.
Update both directories. The main panel now has empty spaces where circuits used to be and the essential panel has circuits with no history; a homeowner or a future electrician reading either one alone will be misled. Write the destination panel beside each vacated space.
Every two-pole load on the carried list takes two adjacent spaces, so the essential panel fills faster than the circuit count suggests — count the positions against the enclosure you were about to order.
The total number of breaker spaces the panel provides.
Each single-pole breaker occupies one panel slot.
Each double-pole breaker occupies two panel slots.
Available panel slots remaining
10 slots
The breakers entered need 30 slots against the 40 this panel has. Being inside the rating on this one check settles nothing about the rest of the circuit — the conductors, the overcurrent device, and the work as installed are all outside it.
- Slots used
- 30 slots
They open the calculator with your figures already in it
Electrical Panel Circuit Directory Slot Calculator: 10 slots — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
What this calculation does not cover
- Spaces left is not capacity left. What may be added to a panel is governed by its bus and main breaker rating measured against a calculated load with demand factors applied, not by empty positions. A 100 A panel with twelve free spaces may have no room for a range or a heat pump at all, and filling the spaces anyway is exactly how a bus gets overloaded while every breaker in it holds.
- There is no place here for a three-pole breaker. In a three-phase panel a 3-pole device fills three spaces, and entering it as a double-pole loses one space every time - on a commercial schedule that is several positions gone by the time the count matters. The panel also has a fixed number of positions per phase, which decides where a three-phase load can physically go, not just whether it fits.
- Breaker spaces are not the only thing a panel runs out of. Every grounded conductor needs its own terminal, since NEC 408.41 permits one neutral per terminal, and equipment grounds, AFCI and GFCI pigtails and multiwire circuits eat bar holes faster than they eat positions. A panel with four spaces free and a full neutral bar needs an added bar kit, and the wire bending space in a crowded gutter is a code dimension in its own right.
Where the Switch Sits Decides What It Must Be Rated For
A transfer switch upstream of the main disconnect is service equipment and has to be listed as suitable for use as service equipment, with the fault withstand, the bonding provision and the enclosure that go with that position. A switch fed from a breaker inside an existing panel is downstream equipment and answers to a smaller set of requirements. The two positions produce quite different bills of material for what looks on a one-line like the same box.
Transfer switches are listed to UL 1008, and the rating that gets skipped is the withstand and closing rating — the fault current the switch can survive while a downstream device clears, and the fault it can be closed onto without welding. It is quoted against a specific upstream protective device, and a switch rated with a particular fuse ahead of it does not carry that rating with a breaker ahead of it instead.
The utility has an interest in this too. Many distribution utilities require a visible, lockable disconnecting means and some require notification of any generating equipment connected on the customer side, whether or not it can ever export. Ask early, because a utility requirement discovered at inspection is a delay measured in weeks and occasionally in a new meter position.
Then look at where the enclosure will physically live. A transfer switch is switchgear hanging on a wall, and a weatherproof enclosure on a west-facing wall in a hot climate cooks its own contactor and its own controller. Shade it, or put it inside, and leave the working clearance in front of it that the code requires — which is not the clearance left after the recycling bins arrive.
The Neutral: Switched, Solid, and the Bond That Follows
Whether the generator is a separately derived system depends on one thing: does the transfer switch switch the neutral. A three-pole switch leaves the neutral solidly connected between the utility, the set and the load. A four-pole switch breaks it along with the phases. Everything about bonding, grounding electrodes and fault-current paths follows from that choice, and it is a design decision made once, deliberately, and recorded.
With a solid neutral, the set is not separately derived. The system bonding jumper stays where it always was, at the service, and there must be no second neutral-to-ground connection anywhere — which includes inside the generator. A great many portable and small standby sets ship from the factory with the neutral bonded to the frame, and connecting one of those through a three-pole switch creates a second bond. Removing it is a documented modification on most machines, and the manual says how.
With a switched neutral, the set is separately derived and needs its own system bonding jumper at the generator and its own grounding electrode conductor run to the building's grounding electrode system. Leave that out and a fault at the set has no low-impedance path home; the overcurrent device sits there while metalwork stays live.
Two bonds is the more common error and the more insidious. Neutral current then divides between the neutral conductor and every equipment grounding conductor and metallic path in parallel with it, which means current flowing on conduit, on water pipe, on structural steel. Ground-fault protection sees an imbalance and trips for no traceable reason, residual devices become unreliable, and nothing about the installation looks wrong to a visual inspection.
On services with ground-fault protection the choice narrows. A solid neutral gives returning fault current a path that bypasses the sensor and produces nuisance operation nobody can explain; a four-pole switch is standard practice there. Where the set carries its own on-board residual devices, confirm how the manufacturer intends them to behave in the bonding arrangement you have chosen — an unbonded set with residual protection on its outlets is a combination that behaves differently from what the label suggests.
The Feeder, the Inlet and the Cord
Between the transfer switch and the essential-loads panel runs a four-wire feeder: two ungrounded conductors, a neutral, and an equipment grounding conductor. The neutral and the grounding bars in that subpanel stay separate and the bonding screw stays out of it, because the bond lives at the service and only at the service. Fitting the bonding screw in a subpanel is the single most common defect on this kind of work and it produces exactly the parallel-path problem described above.
Size the feeder against the transfer switch rating and the load it actually carries, and route it as though it will be inspected, because it will be. Where the switch is outdoors and the panel indoors, the transition needs a listed fitting and the conductors need a wet-location rating for the whole outdoor portion — the inside of an outdoor raceway is a wet location whatever the weather has been doing.
For a portable set the connection point is a power inlet box: a flanged inlet, weatherproof, mounted where the cord will not run through a doorway that has to close on it and where nobody reverses a car over it. Match the inlet, the cord ends and the generator outlet as a set, in one configuration, and hand the owner a cord that fits nothing else in the house.
The cord is the weakest component in the installation and the one that lives outdoors in the wet, gets dragged across gravel and gets coiled while hot. Size it against the current it will carry over its full length, not against the socket it plugs into, and keep it as short as the layout allows. A cord that runs warm is a cord that is undersized, and the owner will not notice until the jacket has already hardened.
The feeder to an essential-loads panel and the inlet circuit for a portable set are both modest, ordinary circuits, and starting from the switch rating gives the conductor size that everything else in the enclosure has to accept.
The amp rating of the breaker this wire will serve.
Minimum wire gauge
12 AWG
This is ampacity-only sizing — long runs may also need a thicker gauge to control voltage drop (see the Wire Gauge Voltage Drop Calculator).
- Ampacity of recommended gauge
- 20 A
They open the calculator with your figures already in it
Amperage to Wire Gauge Calculator: 12 AWG — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 12 AWG — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Copper on the 60 °C column, and nothing else. There is no input for conductor material or insulation rating, so aluminium — which carries less than copper at the same gauge — comes out undersized, and 75 °C or 90 °C rated cable comes out conservative even where every termination would allow the higher column.
- No derating is applied. Ambient temperature above the table's basis, several current-carrying conductors bundled in one cable or raceway, and sun-exposed rooftop runs all cut a conductor's usable ampacity below the table figure, and none of those conditions is an input here. The gauge returned is a floor for ideal conditions, not a finished answer.
- Run length and voltage are not part of this calculation. A 3 m run and a 60 m run at the same amps return the same gauge, and on a long run voltage drop, not ampacity, is usually what sets the size.
- This is not a load calculation and not a circuit design. It converts an amp figure you supply into a conductor size; it does not work out what that figure should be, does not apply the continuous-load 1.25 uplift for you, and does not size the neutral, the equipment grounding conductor or the overcurrent device. Motor, air-conditioning and welder circuits follow their own sizing rules and their nameplate ratings rather than a straight table lookup against running current.
- The table ends at 1 AWG (110 A). Anything needing 1/0 or larger — most services and main feeders — plus parallel conductor sets and the reduced-size allowance the code gives dwelling service conductors, is outside what this returns; a figure above 110 A does not get a valid answer here.
The Electrode, and What It Is Actually There For
A grounding electrode does not clear faults. Soil is far too resistive a path for a fault current to return through, and no rod driven anywhere will operate a protective device. What the electrode does is stabilise the system's voltage to earth and provide a path for lightning and surge energy, and confusing the two purposes is behind a great deal of bad practice on generator installations.
A permanently installed set that is separately derived gets a grounding electrode conductor connected to the building's grounding electrode system — the same system the service uses. Driving an isolated rod at the generator pad and stopping there creates two earth references at different potentials with metalwork bridging them, which is a worse condition than the one it was meant to solve.
Rod resistance itself is set by soil resistivity, driven depth and rod diameter, and depth dominates by a wide margin. Doubling the length of a rod helps considerably; doubling its diameter barely moves the number. On rocky or sandy sites where a single rod cannot reach a useful figure, multiple rods spaced at least their own length apart, a ring conductor or a concrete-encased electrode are the real options — a second rod driven a metre from the first is largely wasted metal.
A portable set connected through an inlet box is bonded to the building's grounding system through the cord's equipment grounding conductor, and that is the path a fault will use. A rod driven beside a portable machine adds nothing to it, and where the frame bonding is in any doubt the rod encourages the belief that the problem has been dealt with.
Driven depth moves the resistance figure and rod diameter barely does, which is worth seeing on a site where the first rod refused at a metre and somebody is proposing a thicker one.
How strongly the surrounding soil resists electrical current flow.
The length of the ground rod actually driven into the earth.
The rod's outer diameter.
Estimated ground rod resistance
39.9 Ω
Soil resistivity varies significantly with moisture, temperature, and composition — use a field-measured value (e.g. Wenner four-pin test) for your actual site rather than an assumed value. NEC 250.53(A)(2) requires a single rod to test at 25Ω or less, or a second rod must be added; this calculator estimates the resistance, it does not replace an actual field measurement.
They open the calculator with your figures already in it
Isolated Ground Rod Earth Resistance Calculator (Dwight's Formula): 39.89 Ω — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 39.9 Ω — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Dwight's formula assumes one uniform soil for the full depth of the rod, and real ground is layered. A wet clay skin over dry sand, or two feet of topsoil over rock, cannot be reduced to a single resistivity — and if the rod refuses on rock at 1.2 m then the length in the formula is 1.2 m, not the 2.4 m of steel that was bought. A Wenner traverse at several pin spacings reveals the profile; one number conceals it, and the error runs to a factor rather than a percentage.
- Resistivity is seasonal, and the shallow soil moves the most. It climbs steeply as ground dries and again as it freezes, where it can rise by an order of magnitude, so the upper metre — the part that dries and freezes — contributes least at exactly the times it is needed. A rod that measures 20 Ω after spring rain can be well past the 25 Ω threshold in February or in a drought, which is why driving below the frost line does far more than diameter ever will.
- One isolated rod. Add a second and the resistance does not halve, because the two current fields overlap — set them closer than the driven length apart and the pair behaves more like a single larger electrode than like two in parallel, which is the reason a minimum separation exists at all. Nor does this see the rest of the electrode system: a concrete-encased electrode, a metal water service or bonded building steel sits in parallel with the rod and usually dominates whatever a fall-of-potential or clamp-on test actually reads.
- A low rod resistance does not clear a fault. On a grounded AC system the fault current returns to the source along the equipment grounding conductor, and the earth is explicitly not permitted to serve as that path — a flawless 5 Ω rod will not operate a breaker. The rod is there for lightning, for static and for holding the system's voltage reference, so ohms in the ground are no substitute for a continuous low-impedance bonded return.
Run Time, Refuelling and the Second Day
Consumption follows load and not rating, so a set carrying a third of its capacity through a mild outage will run much longer on a tank than the specification sheet implies, and the same machine carrying heating and a well pump through a February night will not. Owners plan around the number on the brochure. Give them the number for their own carried-load list.
Fuel type changes the shape of the question entirely. Natural gas has no tank and no refuelling, so run time is unlimited and the constraint moves to the meter and the utility's willingness to upgrade it. Propane has a tank, and a trap: the tank has to boil liquid into vapour fast enough to feed the engine, and the vaporisation rate falls with both the liquid level and the ambient temperature. A large tank at twenty percent in a cold snap can be unable to deliver the vapour the set demands while still holding a substantial quantity of fuel, and the engine will hunt and stall with a gauge showing plenty.
Diesel brings storage problems of its own. Fuel degrades, water condenses in a part-full tank, microbial growth blocks filters, and a set that has sat on the same fuel for four years fails on its filter within the first hour of the outage it was bought for. Fuel polishing, a proper tank vent and a documented replacement interval are maintenance items that only ever get skipped by the person who has not yet had the failure.
Refuelling a portable set is the part of the whole installation most likely to cause a fire. The engine is hot, the exhaust is hotter, and petrol vapour finds it. Shut down, let it cool, refuel away from the machine, and store fuel somewhere that is not the attached garage. Hand this over verbally as well as in writing.
Burn rate at the load the carried-list actually produces is what turns a tank size into a number of hours, and the owner will plan their outage around that figure whether or not anybody gave it to them.
The generator's fuel tank size.
Check the manufacturer's fuel consumption chart at your expected load percentage.
Estimated runtime
6.67 hours
Actual runtime varies with load percentage, fuel type, temperature, and altitude — check your specific generator's published fuel consumption chart at your actual expected load for a more precise figure.
They open the calculator with your figures already in it
Generator Fuel Runtime Calculator: 6.67 hours — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
What this calculation does not cover
- Treats the burn rate as constant for the whole run. Real load moves as pumps, fridges and heaters cycle, so this holds only if the rate you entered is the average across the run rather than the figure at one load point.
- Assumes every drop in the tank reaches the engine. Fuel pickups sit above the tank floor, low-fuel cut-out and surging arrive before a tank is dry, and a propane or LPG vessel is filled to a working fraction of its nameplate size — usable fuel is always less than stated capacity.
- No derate for site or engine condition. Altitude, intake air temperature, fuel type and a worn or poorly serviced engine all move consumption away from the manufacturer's chart, which is measured on a new set under test conditions.
- This is not a sizing or load calculation. It does not check that the generator can carry the load you intend to put on it, and it cannot tell whether the burn rate you entered matches that load — read the rate off the consumption chart at the load percentage you will actually run.
- Ignores the stops a long run needs. Oil-level checks and oil-change intervals on portable sets arrive well before a large tank empties, and refuelling means shutting the engine down and letting it cool. The hours here are fuel-limited, not the hours the machine will run unattended.
Exercise, Batteries and the Failure That Only Appears in an Outage
Standby plant fails in a characteristic way: it works perfectly for four years of monthly exercise runs and refuses to start on the one night it is needed. The starting battery is the cause more often than everything else combined. A battery charger that stopped working eighteen months ago leaves a set that cranks fine during a warm exercise run and cannot turn a cold engine over in January.
Set the exercise regime deliberately. A short weekly no-load run keeps oil moving and confirms the controller and the starting circuit; a longer periodic run under real load is what proves the machine. Diesel sets in particular dislike sustained light loading, and an exercise regime consisting only of unloaded runs builds up exactly the condition that stops the set performing when it is finally asked for full output.
Automatic transfer controllers carry a set of timers and thresholds nobody revisits after commissioning: the voltage and frequency limits at which the utility is declared lost, the delay before starting so a momentary blink is ignored, the delay before transferring, the delay before returning once utility has come back, and the cooldown run afterwards. Defaults are usually sensible and occasionally wrong for a specific site — a rural feeder with frequent brief dips needs a longer start delay than a suburban one.
Carbon monoxide is where portable sets kill people, and it happens after storms, in numbers. A machine in an attached garage with the door open still fills the house. Running it under a deck, near an open window, or in a breezeway does the same more slowly. The instruction is simple and has to be given every single time: outdoors, well away from doors, windows and vents, with the exhaust pointed away from the building.
Proving the Transfer
A commissioning test that consists of pressing the test button on the controller proves the controller. Simulating an actual loss of supply proves the installation. Open the utility supply at its own disconnecting means, let the sequence run without touching anything, and time each stage against what the controller is set to.
Then verify the things that only show up under load. Voltage between neutral and ground at the essential panel should be small and stable — a significant reading with the set running says a bond is in the wrong place or a neutral is carrying current it should not. Check every circuit on the carried list actually comes alive, because a circuit that was marked carried and never physically moved is a defect nobody discovers until the outage.
Finish with the handover pack. A one-line drawing, the carried-load list as built, the bonding arrangement stated in words, the controller settings, the exercise regime, the fuel type and expected run time at the tested load, and a laminated operating sequence at the panel. The next contractor to touch this installation will otherwise re-derive all of it, and more likely will assume it.
- Confirm the neutral arrangement on paper first: three-pole or four-pole, where the single system bonding jumper sits, and whether the set's factory bond has been removed.
- Open the utility supply at its own disconnecting means so the controller sees a genuine loss, and start a stopwatch.
- Time the start delay, the crank, the time to reach stable voltage and frequency, and the transfer itself against the controller settings.
- With the set carrying load, measure line voltage and frequency at the essential panel and the voltage between neutral and ground.
- Switch on and confirm every circuit on the carried list, one at a time, including the ones the owner will only use at night.
- Restore utility supply and time the return delay and the cooldown run, confirming the set stops on its own.
- Leave the one-line, the carried-load list, the bonding statement, the controller settings and the operating sequence at the panel.
The handover pack for a transfer installation
Six things belong at the panel when you leave. Each one is something the next person would otherwise guess at, and guessing wrong on any of them is a hazard and not an inconvenience.
- The carried-load list, marked circuit by circuit as built — Signed off with the owner against the actual directory, including everything deliberately left behind and why.
- A one-line showing both sources and the switching arrangement — Interlock, manual switch or automatic switch, its position relative to the service disconnect, and its ampere and withstand ratings.
- The neutral arrangement, written in words — Three-pole or four-pole, where the single system bonding jumper sits, and confirmation that any factory bond in the set was removed or retained on purpose.
- Grounding electrode arrangement and the measured resistance — Connected to the building's electrode system, never an isolated rod; record depth, number of rods and spacing along with the reading.
- Fuel type, tank quantity and run time at the tested load — Propane installations need the vaporisation caveat stated: a cold, part-full tank can starve the engine with fuel still in it.
- Controller settings and the exercise regime — Start delay, transfer and retransfer delays, cooldown, and whether the periodic run is loaded — an unloaded-only regime stores up trouble on a diesel set.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.