Generator earthing

[Diver300]

I've come across a portable generator with two 13 A UK sockets. The generator can produce a bit over 3 kW.

The 230 V output is floating, so neither the live nor the neutral is connected to ground. The live - earth voltage or the neutral - earth voltage will reduce to near zero if a moderate load is connected between live and earth or neutral and earth, and the generator output will stay working. In that respect it's like many inverters or shaver sockets, and as with supplies from those, a fault to earth isn't going to create more than a tiny current, so there's no need for earth leakage protection.

The odd thing is that the earth on one of the sockets is connected to the frame of the generator, while the other socket, on the other side of the generator, doesn't appear to have any connection to the earth pin at all.

Is the generator safe like that? Are there any plausible fault that could be dangerous? If so, what could be done to make is safer?

 

[Pommie]

Wouldn't the safe route be to bind the earth and neutral terminals to an earth rod and install an Earth Leakage Circuit breaker or a live/neutral imbalance breaker (not sure of the term anymore). Otherwise the generator will happily electrocute someone without tripping anything. Would a live/neutral imbalance breaker trip without an earth rod? Any current to the earth pin will create an imbalance. You'd still get electrocuted by a direct live neutral connection but I don't know any way to stop that.

Mike.

 

[rjenkinsgb]

Is the generator safe like that? Are there any plausible fault that could be dangerous? If so, what could be done to make is safer?

There are HSE rules covering generators - see the Low voltage single phase transportable section in the document below.

It appears all socket earth connections must be electrically bonded to the generator chassis, as per paragraph (2) of that section.

OC 482/2: Electrical safety of independent low-voltage ac

OC 482/2: Electrical safety of independent low-voltage ac

www.hse.gov.uk

 

[Diver300]

Wouldn't the safe route be to bind the earth and neutral terminals to an earth rod and install an Earth Leakage Circuit breaker or a live/neutral imbalance breaker (not sure of the term anymore). Otherwise the generator will happily electrocute someone without tripping anything. Would a live/neutral imbalance breaker trip without an earth rod? Any current to the earth pin will create an imbalance. You'd still get electrocuted by a direct live neutral connection but I don't know any way to stop that.

Mike.

I was thinking along the lines of your suggestion to join earth and neutral and have an ELCB.

An earth rod isn't practical, and anyhow earth rods have too high an impedance to allow enough current to operate over-current protection. They can only pass enough current to trip an ELCB.

Without a low-impedance path from anywhere on the system (generator + loads) to a real ground, there isn't really any much danger if someone touches the generator and ground, so as I see it the important consideration is to make sure that all the bits someone can touch are connected together.

Without a connection between neutral and earth, an ELCB won't trip, but there isn't really any danger for a single fault.

One problem with the floating system is that a single fault can go undetected, meaning that there is a big window of time for there to be a second fault.

 

[sagor1]

Check your electrical code with respect to generators. Here in Canada, the generator "grounding" depends on whether the neutral is bonded to the frame, or floating. The general rule here is that there shall be one and only one earth "ground" in the entire system when tying to the house electrical system. So, depending on type of generator, one has to use the house ground and neutral and not the generator ground, or disconnect the house ground and use the generator ground (with ground rod).
Rules may vary by jurisdiction. Many portable generators have the neutral bonded to the frame. Most home standby generators have a floating neutral. But again, models may vary...
If using a generator externally for portable use (not tied to home system), grounding is recommended.