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mattg4321

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Hi guys, after some advice for a job currently ongoing. I'm fairly inexperienced when it comes to generators, trying to decide whether or not to take this on.

We are currently wiring a domestic new build (mostly!) property (including 4 separate buildings, all with lightings/small power). 90% done on 1st fix and customer has decided she wants a standby generator on the main dwelling (house out in the sticks and gets it fair share of blackouts). Initially I said maybe she could employ someone 'specialist' to supply/fit. She wasn't keen on this as there has been more than one 'specialist' involved in the build and most have turned out to be carp! Said she would rather we do it, as we're known to her and trusted. In the process of deciding whether to fit myself/sub out.

Shouldn't be a huge problem to install. Plant room (intake here and feeds SP house CU via 63A MCB in TPN board) is adjacent to proposed siting of generator. Earthing system is TNCS recently installed. I'm unsure on a few points.

1. Presumably I will need RCD protection for the sub main from plant room to house - when being fed by generator? (something like 100mA time delayed for discrimination?)

2. Do I also need overload protection to prevent the generator being overloaded? (Wholesaler has suggested SDMO 6000E - 6.5KVA along with ATS)

3. Looking at the wiring diagram provided for the generator, it does appear that N and PE are already linked - is this normal? Presumably this can be checked when the generator is run up anyway and if not they can be linked to provide a reference to earth.

4. Once an earth spike has been fitted and connected to generator, should this also be bonded back to MET?

Thanks in advance


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You have a TP and N installation and using a single phase genset then, is that right?
 
Sorry if this wasn't clear. The genset (single phase) is only to supply the main house - which is single phase. When fed from DNO, the house will be fed from a 1P 63A MCB in TPN board in plant room.
 
Hi,
1. How are you provding discrimination between that 63A MCB and the 32A MCBs in the property it is feeding?
2. The linking between N and PE needs very carefull managment, there SHALL BE ONLY ONE LINK N-PE on any system at any time. Places such as the ABB website can be usefull.
3. A generator needs careful care and so on, needs fuel storage and so on.
4. Ask the customer how long and how often are the power cuts and would an inverter supply for essential small loads such as central heating and limited lighting be more cost effective? ( Have a chat with chloride power first)
 
Thanks for your replies.

1. I was always taught that for discrimination, a good rule of thumb is '2 to 1'. I understand that for total discrimination it's probably preferable to use a switchfuse isolator, however that's not really practical here and total discrimination in a domestic setting isn't really a safety issue? I have a C63 MCB feeding max B32 MCB in a CU.

2. Thanks will look at ABB website.

3. She is aware that she will need it serviced and looked after by someone - money isn't and issue really here...

4. Not sure an inverter is going to be suitable here as the power cuts often last for hours at a time. Probably averaging 1-2 a month.
 
Hi,
1. You should contact the manufacturers of the MCBs and ask them, the regs quote 630A to trip the 63A mcb this could easily be exceed by the prospective fault current at the socket outlets, so in that case when there is a short it is a mugs game as to which trips first... The hint is in the flat part of the curve in the regs book, you may wish to reconsider having had the chat with the mcb manufacturere and ask would you be better with a BS88 up stream.

2. Explain to the customer that she needs to expect a break in supply when the main supply fails and the generator takes a little while to start up and settle, also that there will also be a break in supply when the mains returns as the generator can't be used in parell with the supply, syncronisation and the N-E link issue.

3. Cummings standby power would be a good place to look https://www.cumminspower.com/

4. She may still want a 3 kva or more inverter for the essential no break loads.
 
Thanks for your replies.

1. I was always taught that for discrimination, a good rule of thumb is '2 to 1'. I understand that for total discrimination it's probably preferable to use a switchfuse isolator, however that's not really practical here and total discrimination in a domestic setting isn't really a safety issue? I have a C63 MCB feeding max B32 MCB in a CU.

2. Thanks will look at ABB website.

3. She is aware that she will need it serviced and looked after by someone - money isn't and issue really here...

4. Not sure an inverter is going to be suitable here as the power cuts often last for hours at a time. Probably averaging 1-2 a month.


If money isn't an issue why doesn't she get a specialist in to get it right in the first place
 
Thanks for your replies.

1. I was always taught that for discrimination, a good rule of thumb is '2 to 1'. I understand that for total discrimination it's probably preferable to use a switchfuse isolator, however that's not really practical here and total discrimination in a domestic setting isn't really a safety issue? I have a C63 MCB feeding max B32 MCB in a CU.

A rule of thumb isn't really a very good design method,

Presumably you have multiple sub mains being fed from this intake? If so you'd probably be better off with a mccb panelboard to feed them as you can then select and configure the MCCBs to give better discrimination.
Or you may well be able to get bs88 fuse holders for the mcb board you are planning to use anyway
 
you would be better with the main feed for the house being run from an online ups.

main intake- L1 auto changeover

genny - L2 auto changeover


from the autochanger put a ups inplace that will last a min of 5-10mins.

this is to give the generator time to kickin on power failure


why dont you call in a specialist in to work under you? im sure the customer would be happy with this as they trust you
 
A rule of thumb isn't really a very good design method,

Presumably you have multiple sub mains being fed from this intake? If so you'd probably be better off with a mccb panelboard to feed them as you can then select and configure the MCCBs to give better discrimination.
Or you may well be able to get bs88 fuse holders for the mcb board you are planning to use anyway

Take your point. This has been suggested a while ago, but customer wasn't keen on the extra cost/space it will take up as it would need to be in addition to distribution board, as this needs to supply final circuits too. I've not come across fuse holders over about 32A for a distribution board, but will double check to see if they are available. In any case (although it doesn't make it right) you often see this setup in a domestic setting and it rarely(never) causes huge inconvenience in my experience.
 
If money isn't an issue why doesn't she get a specialist in to get it right in the first place

Which is why I suggested this initially. Think I'm going to end up subbing this out/telling her to find someone. Any recommendations in Sussex/Surrey/Kent area anyone?
 
Which is why I suggested this initially. Think I'm going to end up subbing this out/telling her to find someone. Any recommendations in Sussex/Surrey/Kent area anyone?

Get the job done right, get on the phone to Cummins Power on Tuesday.

In terms of incovinence think of it this way, would your posh customer like to be in total darkness because a bulb table lamp which has a BS1362 fuse has gone s/c? If you think this can't happen I have known a B32 in series with a BS1361 15A in series with a 13A BS1362. Hedge trimmer goes through the flex trips the B32 and blows the BS1361 and not touch the 13A in the plug.



As for holders for fuses larger than 32A, I have a 200A bs88 door stop. This size of install is looking more light comercial than domestic, and requires the required experience. I would first call Cummings power and consult with them, you may also want to have a chat with ABB and Schneider as to the design of the mains intakes. You also need to inform the DNO of the generator and or UPS and inform them of the technqiues being used to prevent back feeding of the network.
 

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