A unit with a fault tag on it is not earning. The electrical faults that bring rental generators, light towers and combo units back off rent, and the check-in routine that catches most of them.
A rental unit sitting in the yard with a fault tag on it is not earning anything. That is the real cost of an electrical problem on a light tower or generator — not the part, and usually not the labour, but the days it spends off rent while somebody works out what is wrong with it.
Most of what comes back broken is electrical rather than mechanical, and most of it is the same handful of faults over and over. Rental equipment lives outdoors, gets towed down gravel roads, is plugged in and unplugged by people in a hurry, and spends months at a time in weather. That combination finds every weak termination and every marginal connection you have.
This is written for rental yards, equipment companies and anyone running portable power as part of their business, rather than for someone with one standby set at a shop. If that is what you are after, getting a standby generator ready for a Central Alberta winter covers the other situation.
Roughly in order of how often it turns up.
The single most abused part of any portable power unit. Pins get bent, bodies crack, covers break off, and the whole thing fills with water and dirt. Twist-lock receptacles take the worst of it because people lever cords out at an angle rather than unlocking them.
Watch for pitted or discoloured contacts, which means the connection has been running hot. A receptacle that has started arcing internally will not get better, and the damage usually spreads to the cord cap on the customer’s end as well.
Everything on a towable unit is being shaken constantly. Terminations that were tight when the unit was built work loose over a season, and a loose connection under load generates heat, which loosens it further and eventually damages the termination point itself.
This is the fault that masquerades as something else. It shows up as intermittent output, a breaker that trips for no obvious reason, or one leg reading low. The unit often tests fine in the yard at no load and fails on site under a real load.
Often the most frustrating call, because the unit works in the yard and trips on site. The cause is usually one of: a damaged cord on the customer’s equipment, water in a connection, a genuine fault in what they have plugged in, or a bonding arrangement that does not match how the unit is being used. The last one is covered on its own below because it causes the most confusion.
Breakers on rental units get operated far more than breakers anywhere else, and they wear. A breaker that has tripped hundreds of times is not the breaker it was. Add vibration on the bus and terminations, plus moisture, and the panel is a normal place for faults to live.
The cable run up a mast is flexed every single deployment. Chafe points at the mast guides and where the cable enters the fixture head are predictable failure locations. Add fixture drivers or ballasts, which fail from vibration and heat, and lamp circuits that take a beating every time the mast goes up and down.
If you are running LED retrofits on older towers, driver failures are worth tracking by unit — repeated failures in the same tower usually point at something electrical rather than at bad drivers. The same reasoning applies to building lighting, covered under why high-bay LEDs keep failing.
A unit that will not start is off rent regardless of whether the engine is fine. Charging circuits, battery connections, isolators and the wiring between them are a frequent cause, and the fault is often a corroded or loose connection rather than a dead battery — which is why replacing the battery sometimes fixes it for two weeks.
Selector switches, e-stops, hour meters, gauges and the harness behind the panel. Water gets in, connectors corrode, and harnesses chafe where they pass through the frame. On combo units there is more of all of it in the same space.
This is the one worth understanding properly, because it generates more confused phone calls than anything else on the list.
A portable generator can be built with its neutral bonded to the frame, or with the neutral left unbonded. Both exist, both are legitimate, and which one is correct depends entirely on how the unit is being used — standalone with equipment plugged directly into it, or connected into a distribution system or a building where a bond already exists somewhere else.
The practical consequences are real:
The symptom customers report is almost always the same — “it trips as soon as I plug anything in” or “it worked at the last job” — and the cause is usually that the unit is being used in a configuration different from the one it is set up for.
This is not something to guess at, or to change in the yard because it stopped a nuisance trip. The requirements are specific, they depend on the application, and they are worth confirming against the current Canadian Electrical Code and the authority having jurisdiction for the way your units are actually deployed. Getting it wrong removes protection that somebody is relying on.
Done when a unit comes back, before it goes back on the available list. None of this takes long once it is routine.
On rental equipment the calculation is different from a fixed installation, because the cost of a second failure includes another trip off rent.
Worth replacing rather than repairing: receptacles and cord caps showing any heat damage, breakers that have seen heavy duty, cable with chafe through to the insulation, and any connector body that is cracked. These are inexpensive parts and they are the ones that come back.
Worth repairing properly rather than patching: harness damage, panel terminations, and anything involving the bonding arrangement. A temporary fix on a unit that is about to go out to somebody else is not a temporary fix — it is the next failure, at a customer’s site, with your name on it.
Fleet electrical faults repeat, and the pattern is the information. Worth logging per unit:
Two or three entries in and the problem units identify themselves. A unit that eats drivers, or keeps coming back with the same leg low, has something wrong with it that replacing the failed part is not addressing.
Start with what changed: the customer’s cords and equipment, whether it is wet, and how the unit is connected compared with how it is tested in the yard. Yard testing is frequently at light load into known-good cords, which is the least demanding condition the unit will ever see. Testing under a realistic load before it leaves catches a good share of these.
Possibly, but check the cheap things first. A loose or heat-damaged termination will do exactly this, and so will a worn receptacle on that circuit. Measuring at several points along the path usually finds it quickly, and it is worth ruling out before condemning anything expensive. The same reasoning applies to building systems, covered under phase loss on a motor.
Not as a fix for tripping, no. The bonding arrangement determines whether protection works, so changing it to stop a trip may be removing the protection rather than solving the fault. If a unit trips in a particular configuration, that is worth understanding rather than disabling.
There is no single right interval — it depends on how hard the units work and what they go out to. What matters more is that the check-in inspection actually happens every time, and that terminations get looked at on some schedule rather than only when something fails.
No. Engines, fuel systems and mechanical repair are a different trade. The electrical side — output and distribution, receptacles, breakers and panels, control wiring, charging circuits, mast and fixture circuits, instrumentation and bonding — is what Grasse Electric covers.
Grasse Electric has done electrical service on rental generators, light towers and combo units since 2022, for portable power equipment working across Central Alberta. If you have a unit with a fault nobody can pin down, or you want a check-in routine that catches more before units go back out, call 403-872-8698 or send the details through the service request form. Photos of the panel, the nameplate and anything that looks heat-damaged help a lot.
Related work is covered under generators and light towers, electrical controls and electrical troubleshooting.
Grasse Electric serves Red Deer, Red Deer County, Blackfalds, Sylvan Lake, Penhold, Springbrook, Innisfail, Lacombe, Ponoka and Morningside.
Written by Todd Grasse, Red Seal Journeyman Electrician, Grasse Electric — Red Deer, Alberta. Published October 16, 2026.
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