IT configured back-up genny

[LastManOnline]

A low insulation resistance fault can occur at any time and sit there quite happily on the DNO supply and then cause big problems on the generator.

How would an insulation fault on the DNO supply have an impact on the generator?

 

[davesparks]

How would an insulation fault on the DNO supply have an impact on the generator?

I mean a low insulation resistance fault can occur and go unnoticed while the installation is on the DNO supply.

 

[LastManOnline]

I mean a low insulation resistance fault can occur and go unnoticed while the installation is on the DNO supply.

Ah ok.That makes sense.And that could certainly happen on a non rcd protected circuit.But my situation has more to do with ,not what COULD go wrong ,but with what is MOST LIKELY to go wrong.

 

[davesparks]

Ah ok.That makes sense.And that could certainly happen on a non rcd protected circuit.But my situation has more to do with ,not what COULD go wrong ,but with what is MOST LIKELY to go wrong.

It can happen on an RCD protected circuit too.

 

[LastManOnline]

Generally small (and cheap & nasty) generators have IT operation and usually no RCD (no real point...) as a means of reducing the risk of a fatal shock if in contact.

Ironically I have just received an instruction manuel from the dealer(PRAMAC supplier).Until now I have not had any of my emails replied to as their technical helpline has been "under maintenance".The instructions state that an "insulation monitor" is available if an IT configuration is preferred.Had,nt expected that.Instructions also provide a UK website which I will contact to get their input into my concerns.As always the input from the forum is much appreciated.

 

[pc1966]

Ironically I have just received an instruction manuel from the dealer(PRAMAC supplier).Until now I have not had any of my emails replied to as their technical helpline has been "under maintenance".The instructions state that an "insulation monitor" is available if an IT configuration is preferred.Had,nt expected that.Instructions also provide a UK website which I will contact to get their input into my concerns.As always the input from the forum is much appreciated.

At least in the UK (and possibly ROI) the use of IT supplies and insulation monitoring are only for skilled supervised systems where faults are very likely to be detected and corrected in a timely manner. The usual use-cases include ship electrics and operating theatres where you really don't want avoidable trips on a first-fault.

PRAMAC seems to be a decent company and they do offer LPG generators that have some advantages for backup (long life of stored fuel, difficulty of stealing it if in a fixed tank) so I would hope they could offer you a better arrangement.

Modifying one to have the CPC back to the generator and RCD there is possible but probably an issue for warranty, etc.

In our case we needed a 3-phase generator in a relative hurry (for winter, not in 8-10 weeks lead time on new builds seen just now) and we asked Stephill Generators and they were happy to modify an in-stock model that had sockets to put a 100mA delay RCD on the 400V circuit to suit our hard-wired use. However, making it floating-chassis to mitigate open-PEN risks might not be practical if the AVR is referenced in any way to the 12V DC system that is always to the metalwork due to typical internal combustion engine electrics.

A final option you could consider is one of the open-PEN units for EV support, but you would need to consider how it is connected as probably it has to be powered from the generator and so would need to be 'reset' on start-up and that would make any automatic start/change-over tricky.

 

[LastManOnline]

A final option you could consider is one of the open-PEN units for EV support, but you would need to consider how it is connected as probably it has to be powered from the generator and so would need to be 'reset' on start-up and that would make any automatic start/change-over tricky.

That was another option that crossed my mind but as you say it appears by no means simple to arrange.My next step is to contact PRAMAC and ask them ,regarding my concerns about the situation I,m installing their genny under, is "What configuration would you recommend?"

 

[pc1966]

Is this generator going to be permanently available for automatic backup? If so and you really are concerned about open-PEN risks could it not be put on some sort of insulated raised plinth so in the unlikely event of an open-PEN fault nobody is likely to be in good contact with true Earth at the same time?

 

[LastManOnline]

Is this generator going to be permanently available for automatic backup?

not automatic.Will be connected to installation via a standard C/O switch
and be switched over manually.

f so and you really are concerned about open-PEN risks could it not be put on some sort of insulated raised plinth

yes it could.I,ve given consideration to that too.And of course an insulated plinth would work very well.Also thought about educating the homeowner about how to check for potential open-PEN faults by using a ncv tester before he touches the genny frame.( plus a good pair of rubber gloves!!!).

But essentially I,m looking to carry out the installation in a manner that is 1) safe
2) harmonizes with accespted best practice
3) does,nt compromise the clients warrenty in anyway
4) Does,nt compromise me in any way.

Whats baffling me a little is that I have yet to read in any genny manufacturers literature that "there could be risks associated with an open-PEN scenario "
It could be me of course been a little over sensitive to the possibility.

 

[pc1966]

I'm guessing this is in ROI and I'm aware that there is a "neutralising link" between the supplier's PEN and the local earth rod, etc. However, is it a bit like UK TN-C-S where the N & E are only ever linked in the supply cut-out, or is it more like the USA where there is a N-E link in the first DB?

The reason for asking is the time you need to use a generator is under supply fault conditions and that could well include the open-PEN situation, so if any transfer switch could be isolating the supply PEN and line, leaving the installation on the earth rod and then the generator would also be safe under open-PEN failure of the supply.