Earthing a portable generator

[VicS]

t I have no idea what the test button does: does it replicate a fault, or just verifies that trigger will release the switch. I don't need or want to know.
I'll ask an electrician at the yard.

You ask a question and then say you dont need or want to know the answer. !!!! ?????


The RCD trips when you press the button because an imbalance in the current it senses in the live and neutral conductors is created internally in the way captain boo says. It does not create a leakage to earth but certainly does more than just test the mechanical gubbins.


If you were interested in learning anything about this I would offer you this link http://www.select.org.uk/downloads/BEAMA Installation RCD Handbook V2 2010 updated (2).pdf but as you are not please ignore it but please do ensure that your neutral and earth are connected in the supply from the gennerator.

If the earth and neutral are not connected the RCD will not give you the personal ( or fire) safety protection that it should do.

 

[Deleted member 36384]

... It does not create a leakage to earth but certainly does more than just test the mechanical gubbins. ...... If the earth and neutral are not connected the RCD will not give you the personal ( or fire) safety protection that it should do.

After reading the thread I concluded that I might be getting a false positive when I tested the RCD with the generator connected. This was odd to me because the thread was about the RCDs not working if the generators earth and neutral were not connected - so why does it trip when tested? I was then left wondering if all I had to do was connect the neutral and earth pins to make the RCD protect me. I am not electrically competent beyond wiring a plug up but I wanted to test my understanding before making the connections in the plug, it appears to be a simple solution, if the answer to my post was No, then obviously I was so far out my comprehension that it was not worth proceeding by myself. I also appreciate from the thread that if I connect the neutral and earth then the lead must never be used to connect to shore power.

Thanks for your help. When I am next down at the boat, I will join the earth and neutral pins.

 

[davidpbo]

I was doing site power as a No 2 on an event this weekend using several 3 phase generators in isolation, when the need came to get power from one of the smaller single phase generators powering a towed site lighting stand. It was to give power to a trailer and having enquired of the users whether they had any RCCD protection in the trailer I decided to use an in line one of ours (No RCCD on the generator).

I plugged it in and pressed the test button and nothing happened. Decided to play with my installation tester and check whether it worked if triggered electrically and that did not work either. Got another RCCD and proved that on another (3 phase) genny and distro nearer central stores (I was getting fed up with the walk) and took it back to the small single phase generator. Plugged it in, pressed the Test button and it tripped fine, plugged my tester in and nothing happened. Looked at the tester and the test function was locked out. Looked at the voltages and they were Ph(ase or live)/Earth 117V and Ph/Neutral 234, Neutral/Earth 117V, (Probably ought to be L1 and L2 rather than L and N)

Martindale plug in Tester -- All neons on (Should be 2 outer ones)

If I had wired a plug to that genny such that earth was bonded to neutral it would (I believe) have shorted out half the generator winding with possibly expensive and maybe dangerous results, the Martindale may well have given the correct indication for as long as the generator or fuse worked. The brief tests I did led me to believe that the generator output winding may be centre tapped to earth.

I would be wary of shorting neutral and earth on a generator output without taking more readings and making sure I understood what the results and any circuit diagram were telling me.

I have a basic 2.5KVA framed generator in the garage and intend to do some experimentation with it as to how that is wired. I will post when I have done so.

I was told by someone who should know, that the the "T" button on an RCCD usually only tested the mechanical function (i.e. that the contacts open) which surprised me. To test whether it will open with the appropriate current imbalance usually requires an RCCD tester or installation test meter with the function built in. If I have an old one I may disembowel it to see if there is any electrical connection to the T button.

 

[VicS]

ITYWF that the primary purpose of the test button is to test the mechanical gubbins but it does so by simulating a current imbalance. Certainly did so in the one I disemboweled.

RCD testers do much more allowing different fault currents to be applied, also checking the trip time and some things I dont understand.

See https://www.tlc-direct.co.uk/Book/8.6.3.htm for some info.

I agree that the genny should be checked/ schematic consulted before earthing the "neutral" It'll be interesting to know if your 2,5KVA genny is centre earthed

 

[davidpbo]

Further to my previous post.

I finally had a look at this generator yesterday.

I did this as much for myself as anyone else, to become more familiar with different types of generators and installation testers. The results are what I found with this particular generator, there are many different types of generators and many will be configured differently.

With the generator not running:
There was continuity between chassis of the generator and the earth pin of the 13A Sockets fitted, the Resistance was 0Ω.

I put an earth spike into the ground attached to the chassis of the generator.

There was no continuity between Earth pin and L or N of the socket (Generator not running, fuses/trips engaged) R>200MΩ (Using Insulation test setting on a Metrel Multi Function Tester). L-N was 1.6Ω which looks low for a 2KW Genny but that is resistance not impedance (Which varies with frequency)

Running the generator I got 120V L – E, 120V N-E which would have led me to believe the generator coil was centre tapped to E arth had I not had the previous resistance readings which suggested that it was not.

My MFT would not perform any of the usual tests one would with a domestic installation because the voltages were not what it expected to see, i.e 240ish V L-N and L-E and 0ishV N-E.

A basic Martindale plug in socket tester had all three neons lit instead of the outer 2 one would expect for a typical UK domestic installation.

After a bit of deliberation, as there was no connection I could detect between earth and the generator coil, I did decide to short N-E (through a switch and 1A fuse). The centre neon of the Martindale went out and I was able to perform some of the tests I believe may be carried out when commissioning a domestic installation, however the values obtained were not what one would expect for a domestic installation. Rs (on my meter, I am assuming it is the same as Zs on others) was higher at 5.9Ω, as was Z L-E at 8.8Ω
I would expect something nearer 1/10th of that for a permanent installation but have not measured enough to be sure.

Using RCCBs (Residual Current Circuit Breakers) on the mains output of the generator, they did appear to trip using their built in “T”est buttons with or without the neutral taken to earth. With the N taken to E the installation tester was able to do a more sophisticated function test on them and they all performed as they should, tripping within the correct parameters and not tripping when they should not.

With the generator as supplied (No connection between Earth and Neutral) is hard to see how a fault would trip an RCCD as there has to be leakage from the circuit to cause a current imbalance between L and N and trip the RCCB.

Would I use a RCCB on the output of the generator? Probably, it doesn’t seem to cause any problem and in the event of the cable getting cut or similar it may trip out faster than an over current breaker of doubtful parentage if an earth fault did somehow develop it may be better than nothing but because of the relatively high resistance readings obtained it may not be enough to prevent a painful if not fatal shock. For me if I was using this generator a lot I would source a more sensitive 10ma RCCB. I would also try to use Class 2 (double insulated) appliances where possible, particularly if hand held, e.g. drills and saws.

Would I short the Live to Neutral, probably not, whilst doing so may mean that a UK plug in socket tester gives the right reading for a UK supply it doesn’t necessarily and in my humble opinion, in the instance of this generator make it any safer. My understanding is that an isolated supply either by transformer or off an isolated generator should not give an electric shock for an L or N to Earth fault through someone. Touching L and N simultaneously certainly will!!.

I came across this whilst searching the web for 10ma RCCBs. The RCD Handbook, probably a cure for insomnia if not of interest.

I certainly got the impression with the RCCBs I used that they were being tripped electrically, I did not have one I was prepared to sacrifice. One (on a 63A breaker) the breaker would lock on whether there was power on the input or not, it would only trip out if it was powered when the T button was pressed, one a plug in adaptor and the other a 13A plug would not lock on without power applied.

 

[colind3782]

If it helps, I have one of those generators and the flimsy on/off switch disintegrated. When I went to bridge the wires to use it I found that "making" the connection (to earth) switches it off.

 

[davidpbo]

If it helps, I have one of those generators and the flimsy on/off switch disintegrated. When I went to bridge the wires to use it I found that "making" the connection (to earth) switches it off.

Which is what the switch would do if it is the engine on/off switch, towards the left in my photo and nothing to do with the 240V power side other than sharing the same chassis/earth and ... If the engine don't go there isn't any power generated.

My posting was only concerned with mains output

 

[VicS]

Further to my previous post.

I finally had a look at this generator yesterday.


There was no continuity between Earth pin and L or N of the socket (Generator not running, fuses/trips engaged) R>200MΩ (Using Insulation test setting on a Metrel Multi Function Tester). L-N was 1.6Ω which looks low for a 2KW Genny but that is resistance not impedance (Which varies with frequency)

Running the generator I got 120V L – E, 120V N-E which would have led me to believe the generator coil was centre tapped to E arth had I not had the previous resistance readings which suggested that it was not.

The explanation being perhaps that there are capacitors between each of the output conductors and "earth"

 

[MARNEN]

Having stumbled across this thread last night I decided to try using my 1kw Honda suitcase genny to charge the batteries via the shore power socket, on the boat.
Went to the boat today and started the genny. I connected the earth and neutral terminals in the 13amp plug as suggested earlier in the thread and plugged the other end into the boats shore power socket, all good so far. Just out of interest I put my LAP plug in tester into one of the 13amp sockets in the cabin I got a green and a red led lit up meaning 'live neutral reverse'. , I panicked a bit and unplugged the genny from the boat I then plugged the tester directly into the genny and got the same reading. When I got home tonight I tested the tester in the house electrical socket and got 2green leds lit up to say all is good. What should I be doing to get 2 green leds lit up on the tester from the genny. Genny is a about 8 years old now but has never been a problem starts easily and runs like a dream. Any helpfull advice greatfully received.
Thanks in advance.

 

[VicS]

Having stumbled across this thread last night I decided to try using my 1kw Honda suitcase genny to charge the batteries via the shore power socket, on the boat.
Went to the boat today and started the genny. I connected the earth and neutral terminals in the 13amp plug as suggested earlier in the thread and plugged the other end into the boats shore power socket, all good so far. Just out of interest I put my LAP plug in tester into one of the 13amp sockets in the cabin I got a green and a red led lit up meaning 'live neutral reverse'. , I panicked a bit and unplugged the genny from the boat I then plugged the tester directly into the genny and got the same reading. When I got home tonight I tested the tester in the house electrical socket and got 2green leds lit up to say all is good. What should I be doing to get 2 green leds lit up on the tester from the genny. Genny is a about 8 years old now but has never been a problem starts easily and runs like a dream. Any helpfull advice greatfully received.
Thanks in advance.

difficult to understand why you got a "live neutral reverse" indication when you had linked earth and neutral at the plug.

Boat end of cable correctly wired ?

 

[mattnj]

I have a dedicated generator lead which has its earth and negatives joined inside the plug that goes into the generator. You must not use this lead for a shore power connection!!!

I've never been sure on this....had our supply changed at home a few months ago, and the Neutral having gone through box, meter etc is then joing to the earth anyway, where is comes in from supply.

 

[Richard10002]

difficult to understand why you got a "live neutral reverse" indication when you had linked earth and neutral at the plug.

Boat end of cable correctly wired ?

He said it happens with the tester plugged into the genny socket, so the boat cable isn't in the equation at that point.

Perhaps there has always been this fault inside the genny?

 

[Richard10002]

I've never been sure on this....had our supply changed at home a few months ago, and the Neutral having gone through box, meter etc is then joing to the earth anyway, where is comes in from supply.

That seems to be how it works.. but a genny isn't connected to a supply... it is the supply...

So if earth and neutral aren't connected inside the genny, you need to do it outside the genny in the cable that connects the genny to the boat. However, you must never use this cable for a shore power supply.

 

[MARNEN]

Tried to find the answer today. Firm I bought the generator from had no Idea. Spoke to Honda and other distributors, yet another blank, eventually got a service engineer who seemed to think it was quite normal. His explanation was that it is because it is not earthed internally. I am still looking any more info. The manual has a wiring diagram but even the english version is beyond me.
If any other forumites could test there genny and if they are the same that at least would be comforting.

 

[Strolls]

Came across this article the other day: http://petepower-discussion.blogspot.co.uk/p/normal-0-false-false-false.html

Am very impressed by this Pete Power bloke - he has a long discussion of Honda generators on his site, too: http://www.petepower.co.uk/choosing-generators.html