Trying to ground portable generator

[scottfd]

I’m trying to ground my 3500 watt portable generator. When I plug an electrical tester directly into the generator outlet, it lights up and indicates “no ground”. I went to a electrical store and bought a grounding rod, ground wire, and the adapter needed to attach the wire to the rod, hammered the rod approx 5 feet in the ground and wrapped the other end of the wire onto a nut that is on the frame of the generator but when I plug the tester back into the generator, it still shows “no ground”. Am I doing something wrong here?

I’m trying to get this setup so I can run my gas furnace off of this if needed. The furnace is new and when I tested everything, it ran for about 1 minute and then shut down and gave me a diagnostic code that meant no ground as well. Any help would be appreciated. Thanks!

 

[endoftheworld]

Small gennies tend to be the 'floating earth' design, which means the earth is not tied to neutral. Your house wiring goes back to the substation where earth is bonded to the star point of the transformer, and equalised with ground potential. In your generator there is no electrical distinction between live and neutral except that both are opposed, and neither relates to ground potential, this presents issues for circuit breaking and isolation (i.e. breaking the live does not necessarily isolate the appliance as both conductors are effectively opposite lives). You may also have trouble getting an RCD to trip, the test button will work, but it won't detect a fault unless your earth rod is really well grounded.

Most testers fail to identify polarity on gennys rather than failing to identify earth, but in any case you need to open the front panel of the genny and bond neutral to earth. Fault current will then return to the opposite phase from where it originated (which is where all current wants to go).

Then, for extra safety remove the 2 pole breaker (which is just an MCB) and fit an RCBO, which will now work properly.

I never saw much value in the MCBs on gennys as the trip current is usually 3x higher than rated value so it doesn't actually protect the genny from overload, unless you get a dead short live-neutral. If you want to protect from overload you can get resettable fuses which do actually trip at their rated current.

Genny manufacturers always leave the earth floating on small gensets as they know most people won't earth them anyway, in which case if the earth and neutral were bonded the chassis could develop a potential relative to ground. i.e. live.

All the bigger units, over 10KVA usually are bonded when new. These are normally on skids and have lots of earth contact whether the rod is used or not. Big gennys on trailers should therefore always be earthed.

In theory you should also test your earth rod with an earth resistance tester, if you have access to one.