Isolation Transformer - A discussion

[JohnW2]

Would it be wrong to make any sort of earthing/bonding arrangement to the buildings earth when the temp supply is/can be totally floating .... ?

I'm not sure what you are saying here. If you connect any part of the the "temp supply" to earth then it would not be "floating", would it? Any connection of it to 'an earth' renders the supply earth-referenced (i.e. non-floating).

Kind Regards, John

 

[SUNRAY]

I'm not sure what you are saying here. If you connect any part of the the "temp supply" to earth then it would not be "floating", would it? Any connection of it to 'an earth' renders the supply earth-referenced (i.e. non-floating).

Kind Regards, John

I should have been more carefull and stated earthing/bonding only the temp genset & heaters CPC but leaving the 3ph live conductors floating... As per the majority of this discussion.

 

[Harry Bloomfield]

So the sort of thing I'm refering to in response to your question about generators is this sort of thing, as I get involved with installing 100KVA generators

A colleague to often ring me for advice one such matters and one day rang me to ask my advice on how such a generator ought to be connected regarding whether it should or should not be connected to the factories main earth or be left floating. After many hours discussing the pros and cons, we never arrived at any firm conclusion. I don't know which way he eventually decided to connect it.

 

[JohnW2]

I should have been more carefull and stated earthing/bonding only the temp genset & heaters CPC but leaving the 3ph live conductors floating...

I don't really understand what you're saying. Am I right in thinking that the genny is supply (only) the heaters, and that supply is floating (i.e. not earth-referenced). If so, what is the 3-phase supply you're talking about and what did you mean by "...any sort of earthing/bonding arrangement to the buildings earth"?

Kind Regards, John

 

[SUNRAY]

I don't really understand what you're saying. Am I right in thinking that the genny is supply (only) the heaters, and that supply is floating (i.e. not earth-referenced). If so, what is the 3-phase supply you're talking about and what did you mean by "...any sort of earthing/bonding arrangement to the buildings earth"?

Kind Regards, John

This part of the replies is directly responding to this:

If one had a 240V battery (or generator I suppose) running a single appliance then surely connecting the appliance metal case to the house supply earth would only introduce hazards to the appliance and user?

So this is my interpretation, A generator supplying one appliance, just as EFL introduced.

So the sort of thing I'm refering to in response to your question about generators is; this sort of thing as I get involved with installing 100KVA generators

and 80KW heaters:

Would it be wrong to make any sort of earthing/bonding arrangement to the buildings earth when the temp supply is/can be totally floating and the heater(s) are indoors?

 

[JohnW2]

This part of the replies is directly responding to this: ... So this is my interpretation, A generator supplying one appliance, just as EFL introduced.

Fair enough, but I still don't really understand what is being said/asked (by you), so I can't comment.

Kind Regards, John

 

[SUNRAY]

Fair enough, but I still don't really understand what is being said/asked (by you), so I can't comment.

Kind Regards, John

Really I was asking EFL based on his introduction of the situation.
How should temporary 100KVA generators outside the building

and big temporary heaters, typically 20-80KW inside a building with a fixed and operational electrical installation:

Be electrically installed?
EFL seems to be saying just plug the heater into the generator and no other connexions.

 

[bernardgreen]

temporary 100KVA generators outside the building

is much the same as the secondary of an electrical substation at the end of the road. Treat them both the same way.

 

[SUNRAY]

is much the same as the secondary of an electrical substation at the end of the road. Treat them both the same way.

Do I assume you are saying link the CPC's?

 

[EFLImpudence]

Really I was asking EFL based on his introduction of the situation.
How should temporary 100KVA generators outside the building
and big temporary heaters, typically 20-80KW inside a building with a fixed and operational electrical installation:

I have no experience of such things.

Do they have their own earthing system which may contact the ground - as Bernard says; like a(nother) substation?

EFL seems to be saying just plug the heater into the generator and no other connexions.

I was thinking more of a small (portable as in able to be carried) petrol generator (equivalent to a battery) which might be running an item in a house or garage.

Would you connect it to to the house earth and why and how?

I suppose no one would say if you had a device running off a 12V car battery then something should be connected to the house earth. So, if it were 240V why would it have to be?

 

[SUNRAY]

I have no experience of such things.

Do they have their own earthing system which may contact the ground - as Bernard says; like a(nother) substation?



I was thinking more of a small (portable as in able to be carried) petrol generator (equivalent to a battery) which might be running an item in a house or garage.

Would you connect it to to the house earth and why and how?

I suppose no one would say if you had a device running off a 12V car battery then something should be connected to the house earth. So, if it were 240V why would it have to be?

Ah OK so, as an example, you are saying that using one of these:

to power one of these:

it would introduce significant hazard to link it to the building earth

But to do the same thing with these:

You have absolutely no idea and yet they differ only by size.
Do you have a cut off limit on size where the change occurs?

 

[EFLImpudence]

You have absolutely no idea and yet they differ only by size.

IF size is the only difference, please explain why you would connect the small one to the house earth.

Do you have a cut off limit on size where the change occurs?

I have asked you that question.

If I am wrong and am not aware of something, please explain rather than repeating the same questions.

Obviously if I am unaware of something then I will not be able to answer.

 

[bernardgreen]

Do I assume you are saying link the CPC's?

The substation has it's Neutral Star point bonded to Ground, do the same with the generator if 3 phase, For single phase generator connect one side to Ground via a Ground rod. Deliver power to the load(s) as if it was a PME system TN-C-S a fed from the local DNO Treat the load(s) as you would if the supply was from the DNO.

The CPC of the generator ( or substation ) is Grounded, hence the CPC of the supply ( generator or substation ) and the CPC of the load(s) are connected via the Neutral

 

[Harry Bloomfield]

I was thinking more of a small (portable as in able to be carried) petrol generator (equivalent to a battery) which might be running an item in a house or garage.

Would you connect it to to the house earth and why and how?

The how at least would be to connect one pole to ground/earth and the chassis.

 

[JohnW2]

Really I was asking EFL based on his introduction of the situation. .... How should temporary 100KVA generators outside the building ... and big temporary heaters, typically 20-80KW inside a building with a fixed and operational electrical installation: .... Be electrically installed? ... EFL seems to be saying just plug the heater into the generator and no other connexions.

IF the genny does not have any connection between its output and earth, and if it is only supplying the heaters, then I would think that to do anything other than "just plug the heater into the generator and no other connexions" (particularly, any suggestion that the genny/heaters should be connected to any sort of earth) would merely increase potential hazards.

- so, if you think differently, what would you do, and why?

Kind Regards, John