RCD on TT supply

The Rcbos do not provide fault protection to that cable, earlier posts suggested if Swa cable or earthed containment was used, that it would allow you to remove the RCD', however a fault on that cable would not trip an Mcb leaving the metal swa glands and any metalwork at a dangerous voltage
That's not what I meant, but I understand what you're saying.
 
Sponsored Links
an earth rod has been fitted
Is this allowed with a TT system?
The presence of an earth rod does not make it a TT system
It's exceptionally unlikely that a generator would be configured as TT.

Whether RCDs/RCBOs are required depends on several factors, but they will very likely be for the cable rather than the connected equipment.
 
TT is where the ground is used to transmit the earth, with a generator there is no need to do that, but the problem is with any emergency power supply to ensure nothing dangerous is sent back down the supply line when the back up is in use, so when the DNO worker has isolated and earthed the supply at the origin nothing if fed back from the destination which can injure the worker, this includes using the DNO earthing system once the supply has failed.

The advantage of TT is there is no worry over the DNO worker, but the disadvantage is the RCD is then the primary safety device. As a secondary device no one really worries too much if type AC, A, F, or B, but as primary device that changes.

We also need to consider a gradient between earthing systems, being able to touch two earthing systems with over 50 volt between the two must be avoided, and the design must take this into account. This has caused a big problem with electric car charging, and there have been so new methods used to get around the problem, which 20 years ago would not have been allowed.

I have at work many times been approached and asked how do you do this, and I have given an answer, then maybe 4 months latter visited the home, and realised the description had been warped some what, I the result was not what I would have considered safe.

So you have had a guy on site who has installed an unsatisfactory system which can fail causing flooding and he said this is required to comply with regulations, this does not seem correct, there must be a method where the pump can do its job, we see with life support equipment how in some cases the fuse is not fitted in the 13 amp plug, where some one has done a risk assessment and said having a fuse is too high of a risk.

So it seems likely some thing can be done, and with remote pumping stations we have telemetry to report on faults and special RCD's which can auto reset, but the big question is, on a DIY forum can anyone safely advise what to do? I would say best advise is to get some one on site use to working with this sort of equipment, when I worked for north west water, and SLD pumps we had the infrastructure where we could get specialist advice, including the supply of specialist equipment. So your looking for a firm with water or pump in their name, who can send some one out to advise.

To use advise from the forum which includes me, could result in danger, either from flooding or from electric shock, it is just too easy to imagine what you have and get it wrong.
 
Sponsored Links
That's good advice ericmark. Unfortunately the generator installer isn't local, probably a mistake, but it is what it is. Incidentally, the whole of the outbuilding installation is on a TT system, not just the standby generator.
 
.... As the building is remote from the main house which is PME, an earth rod has been fitted. The electrician has fitted a 32A 30mA RCBO in the fuse box to supply the ATS unit. The ATS then feeds three 6A RCBOs for the pumps and one 16A RCBO for a socket and light in the generator shed. ... The problem I have is that if any one pump has a fault, it is likely to trip the main 32A RCBO which would flood the building. There are voltage and float alarms and such like, but no good if no one is in. ... to get to the point, can I change the 32A RCBO which supplies the ATS to an MCB?
Quite aside from the discussion about whether the cable feeding the outhouse requires RCD protection (which I doubt that it does), I would have thought that, rather than changing the 32A RCBO to an MCB, you could change it to a 32A time-delayed RCBO, which would not trip if one of the 6A ones did.

Having said that, perhaps because I've never had need to look for one, I'm not sure whether or not time-delayed RCBOs actually exist. However, time-delayed RCDs certainly do, so you could (if you couldn't get a TD RCBO) use one of those together with a 32A MCB.

Kind Regards, John
 
More of a question to an answer, where does it say an ordinary person needs type tested equipment, I have been told it does, but not found the law or regulation.

You can get RCD/RCBO which you can set delay and current, I was using these in early 90's, they have been around for years, often they are an add on to a moulded breaker or MCB, I could set up to 1 amp at 5 seconds, although when some one put a nail through a cable tripped 5 RCD's at varying current and amps.

So the question is more what is allowed than what can be done, be it a RCD or moulded breaker or rewireable fuse, I have been told not allowed to have a device where the user can set delay, or current, is not permitted when an ordinary person is in control.

Having an electrician on contract means ordinary person not in charge, or of course if some one is instructed or skilled. But since I am skilled I have never worried about how to be classed as instructed or skilled.

We saw with court case of Emma Shaw's death how the court did not consider the electricians mate as instructed, so I can see why any one would have second thoughts on installing a RCD with a delay.

There is a combined RCD and monitor that warns when it approaches the trip current, it was called X-Pole and when I hunt for it I find dancing girls.
 
Eaton make them called a Type G with a 10ms delay, though its unlikely to fit most boards, so not much point in this case https://www.eaton.com/gb/en-gb/cata...bined-rcd-mcb-device-pkn6-pknm--1-n-pole.html
Thanks. I suppose it's just about enough, but a 10ms delay is not very much. The demand for TD RCBOs is probably so small that it's not surprising that I hadn't seen or heard of any! On the rare occasions on which there actually is a 'need', one can, as I said, simply use a TD RDD plus an MCB.

Kind Regards, John
 
More of a question to an answer, where does it say an ordinary person needs type tested equipment, I have been told it does, but not found the law or regulation.
BS7671 actually says extremely little about 'type tested' at all (let alone in relation to 'ordinary persons') - I think only in relation to domestic CUs, certain types of busbar assembly and Class II items.
You can get RCD/RCBO which you can set delay and current ... So the question is more what is allowed than what can be done, be it a RCD or moulded breaker or rewireable fuse, I have been told not allowed to have a device where the user can set delay, or current, is not permitted when an ordinary person is in control.
Indeed - that is something which BS7671 does say, more than once. However, it's a bit ineffective/half-hearted, since that 'prohibition' only applies if the setting of delay or current can be done "... without a deliberate act involving the use of either a key or a tool".

Kind Regards, John
 
There are units that auto reset temprcd.jpg the problem is cost, around £200.
 
There are units that auto reset .... the problem is cost, around £200.
Yes, they exist, but the cost is far from being 'the problem'. Such devices clearly have absolutely no place in any domestic environment (and probably not in a DIY forum!).

Indeed, even in a non-domestic environment, I would think that they could/should only be used with extreme caution, and only in situations where there is a 'very good reason' (which outweighs the risks). In case you are tempted to start talking about their "being under the control of instructed and skilled persons" in a non-domestic environment, I think that would be irrelevant. The whole point of "auto reset" is surely that the devices are able to 'act' (potentially creating hazards) when they are not "under the control" of anyone, isn't it?

Kind Regards, John
 
Yes, they exist, but the cost is far from being 'the problem'. Such devices clearly have absolutely no place in any domestic environment (and probably not in a DIY forum!).

Indeed, even in a non-domestic environment, I would think that they could/should only be used with extreme caution, and only in situations where there is a 'very good reason' (which outweighs the risks). In case you are tempted to start talking about their "being under the control of instructed and skilled persons" in a non-domestic environment, I think that would be irrelevant. The whole point of "auto reset" is surely that the devices are able to 'act' (potentially creating hazards) when they are not "under the control" of anyone, isn't it?

Kind Regards, John
Not really a problem it does test to see if earth fault corrected before they reconnect, in the main used in remote pumping stations, not even sure why they even have a RCD to be frank, but that does seem to be the point here, a risk assessment considers the risks, and puts them in order, so should some thing go wrong, one can show one considered all the risks.

But of cause to do a risk assessment first you need the method statement, i.e. you say how it is all designed to work, so in this case if all done in one of the protected cables in the list, likely SWA the need for RCD protection does not seem to be there to start with?

But what we are looking at is what happens if it all goes wrong. I can see the court case in minds eye, two electricians said needs RCD and some guys on forum said it did not seem necessary, so with no electrical training I took it upon my self to remove it. Can't see that going down well.

This is why we have to pay for experts, so domestic electrician said needs RCD and specialist pump electrician says risk assessment has been done and not required is going to be seen in a very different light.
 
Not really a problem it does test to see if earth fault corrected before they reconnect,...
I don't know enough about how they do that 'testing' to really comment, but the general concept of any protective device which is able to 'reset' itself (without any human involvement, whether by 'instructed and skilled' people or not) make me pretty nervous.
... in the main used in remote pumping stations, not even sure why they even have a RCD to be frank ....
One does wonder - not only about why they feel the need for an RCD but also how likely they consider it that the RCD will operate when there is not an ongoing need for it to operate (and 'stay operated')!
But what we are looking at is what happens if it all goes wrong. I can see the court case in minds eye, two electricians said needs RCD and some guys on forum said it did not seem necessary, so with no electrical training I took it upon my self to remove it. Can't see that going down well.
You're seem good at thinking about hypothetical court cases, even though I don't think we've every heard of one (relating to electrical installations) in the UK that has resulted in a particularly significant sentence/penalty :)

In this particular case, I wouldn't have thought that a court would have any real problem, since BS7671 is very clear about what cables do and do not require RCD protection - so, in this case, I rather suspect that the court would end up deciding that it was the "two electricians" who were 'wrong'.

Kind Regards, John
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top