PME carport

[pc1966]

So I figure that the carport being TT and having all of the posts bonded is no worse than the carport not having power supply inside it, as posts are close to PME earth in the ground.

That would be my take on things, but worth checking.

If you only need a small amount of power then the simplest option is a TT supply fed from a 13A plug in the house. Not too expensive to put in a small garage CU for it, and no Part P to worry about. Ultimately the metalwork is no less safe than it currently is in respect to the risk from nearby PME faults.

 

[marcuswareham]

That would be my take on things, but worth checking.

If you only need a small amount of power then the simplest option is a TT supply fed from a 13A plug in the house. Not too expensive to put in a small garage CU for it, and no Part P to worry about. Ultimately the metalwork is no less safe than it currently is in respect to the risk from nearby PME faults.

Yes I was going to spur out of C/U on one of the socket rings and do a minor works cert for it.

I might put a new circuit in and notify building regs, but shall see.

Just can't seem to get a straight answer from the council's documentation about if changing from TN-C-S to TT would be notifiable

Yes think TT is the way to go, getting that earth rod as far away from the gas pipe as I can.

Thank you very much for your advice,

 

[Wilko]

Hi - for what it’s worth, my understanding is a change to the installation’s earthing arrangements is not a notifiable activity in England.

 

[pc1966]

I guess if your CU is already all-RCD then it is simply a matter of changing how the MET is connected to "earth"

 

[shaun1]

If the water pipe is plastic then would it help to change the gas pipe to plastic also (even just a small section where it enters the house?

 

[westward10]

You cannot have a plastic gas pipe entering a property, think about the risks.

 

[marcuswareham]

I guess if your CU is already all-RCD then it is simply a matter of changing how the MET is connected to "earth"

I have a memera 2000 split C/U. However I do have RCD protection on all circuits, I have a sub C/U for electric shower containing RCD, and down stream RCDs for lighting circuits.

They are all rated at 30mA and I have done disconnection time on all of them and they are within spec. If changing to TT would I not also need a 100mA RCD for the whole system. Also what to do with the DNO (TN-C-S) earth from the service head just terminate it?

 

[pc1966]

Yes, if you have any non-RCD circuits at all then you would need an overall RCD to meet disconnection times on them. To achieve discrimination with your 30mA ones it would have to be a higher current (e.g. 100mA) and a delay S-type.

As far as I understand it, you should not touch the DNO cut-out so if changing the cable I would simply put a terminal block or similar on the end removed from your MET to insulate it and label things so anyone in the future knows why it was disconnected.

 

[marcuswareham]

Yes, if you have any non-RCD circuits at all then you would need an overall RCD to meet disconnection times on them. To achieve discrimination with your 30mA ones it would have to be a higher current (e.g. 100mA) and a delay S-type.

As far as I understand it, you should not touch the DNO cut-out so if changing the cable I would simply put a terminal block or similar on the end removed from your MET to insulate it and label things so anyone in the future knows why it was disconnected.

Yes fair enough,


All this has also got me thinking about my outside lights, I have 2 class I each side of my front door at about shoulder height. That is probably not a good idea being PME hahaha

 

[Ian1981]

Yes fair enough,


All this has also got me thinking about my outside lights, I have 2 class I each side of my front door at about shoulder height. That is probably not a good idea being PME hahaha

Class 2 are non metallic.
opps 2 class 1 doh!!??‍

 

[pc1966]

All this has also got me thinking about my outside lights, I have 2 class I each side of my front door at about shoulder height. That is probably not a good idea being PME hahaha

To be fair PME faults are not very common, and the real risk is for stuff that people are likely to be in good contact with while also outside. Electric cars being washed while on charge are an obvious risk, metal caravans on nice wet grass, boats on marinas being fed power while engines off, etc.

I guess most outdoor power or gardening tools these days are double insulated so no earth to worry about.

Thought there was a school fence that gave some kids shocks (thankfully none fatal) in the news not that long ago, so it is not unknown!
[automerge]1586604142[/automerge]

I have a memera 2000 split C/U. However I do have RCD protection on all circuits, I have a sub C/U for electric shower containing RCD, and down stream RCDs for lighting circuits.

Is the sub-CU fed from the main one, or split meter tails?

If fed from the main one, is the main switch one that could simply be replaced with an RCD?

 

[marcuswareham]

To be fair PME faults are not very common, and the real risk is for stuff that people are likely to be in good contact with while also outside. Electric cars being washed while on charge are an obvious risk, metal caravans on nice wet grass, boats on marinas being fed power while engines off, etc.

I guess most outdoor power or gardening tools these days are double insulated so no earth to worry about.

Thought there was a school fence that gave some kids shocks (thankfully none fatal) in the news not that long ago, so it is not unknown!
[automerge]1586604142[/automerge]

Is the sub-CU fed from the main one, or split meter tails?

If fed from the main one, is the main switch one that could simply be replaced with an RCD?

Yeah I hear what you are saying about limited risk, I guess the easiest option is to move the lights higher up, so the risk is even less, unfortunately I cannot do that, but I will not lose sleep over it just yet.

Maybe there needs to be a device like the matt-e thing which offers a little more protection by measuring the voltage but which fits in a single gang backbox, for use for outside sockets with low demand etc feed from F.C.Us

The sub C/U is feed from a 40A MCB from non RCD side of the main C/U, so yes replacing main switch with a RCD would be an option although I am limied as you cannot get the MEM breakers for my C/U anymore, doh

 

[pc1966]

The sub C/U is feed from a 40A MCB from non RCD side of the main C/U, so yes replacing main switch with a RCD would be an option although I am limied as you cannot get the MEM breakers for my C/U anymore, doh

Ah, that sucks A quick search found this 2nd hand one, the earth tail is cut short but it might just be worth a try if you have a MFT to check the trip characteristics, etc, on some simple test bed before deciding if it could be fitted:

MEM RCD 100 Amp 100ma Double Pole 100a Time Delay RCCB MEMERA 2000 A100MET for sale online | eBay UK

Find many great new & used options and get the best deals for MEM RCD 100 Amp 100ma Double Pole 100a Time Delay RCCB MEMERA 2000 A100MET at the best online prices at eBay UK! Free delivery for many products!

www.ebay.co.uk

Failing that the obvious solution is a new CU but that opens a whole can of part P worms...
[automerge]1586606757[/automerge]
Or you could fit a small metal enclosure with a separate RCD in it. I think I have seen isolator switch & SPD combinations so why not RCD?

Yes, it is separating the meter tails and without an isolator switch you are in to the dodgy business of getting the DNO to pull the fuse (if it did not "fall out" accidentally...) but it is another way that avoids a new CU for now.

 

[marcuswareham]

Ah, that sucks A quick search found this 2nd hand one, the earth tail is cut short but it might just be worth a try if you have a MFT to check the trip characteristics, etc, on some simple test bed before deciding if it could be fitted:

MEM RCD 100 Amp 100ma Double Pole 100a Time Delay RCCB MEMERA 2000 A100MET for sale online | eBay UK

Find many great new & used options and get the best deals for MEM RCD 100 Amp 100ma Double Pole 100a Time Delay RCCB MEMERA 2000 A100MET at the best online prices at eBay UK! Free delivery for many products!

www.ebay.co.uk

Failing that the obvious solution is a new CU but that opens a whole can of part P worms...

Ahh thats the puppy, yes I have MFT and I spend alot of my working life testing RCDs so thats fine :- D

Yes I have before now though it might be time for a new C/U, I will wait until I need to do other additions etc, then kill all the birds with one stone

Just had another thought on the outside lights, Another workaround could be to use B22 12v bulbs in the fitting and supply the fittings via a 12v transformer, providing electrical isolation and extra low voltage, so no need for the earth bond, and no risk of touch voltages, maybe :- S

 

[pc1966]

If there is any simple way to TT supply the whole house and car port then all of the PME risk problems go away in one step.

I would try to ascertain if the service pipe work is bonded to the PME of neighbours first as that would negate any TT benefits. Some gas pipes now have insulated sections for this reason, and often the gas main is plastic even if the pipework in to the home is metal, so you might be OK there. Otherwise the trouble of sorting gas pipes is way too much and unlikely to be done during lock-down as not essential work!

 

[marcuswareham]

If there is any simple way to TT supply the whole house and car port then all of the PME risk problems go away in one step.

I would try to ascertain if the service pipe work is bonded to the PME of neighbours first as that would negate any TT benefits. Some gas pipes now have insulated sections for this reason, and often the gas main is plastic even if the pipework in to the home is metal, so you might be OK there. Otherwise the trouble of sorting gas pipes is way too much and unlikely to be done during lock-down as not essential work!

Yes I agree,

I am not on mains gas nor is any of the village, so the metal gas pipe runs to a shared (with neighbours) gas bottle storage which is bonded to all services supplied from it, Although that said bottled gas is so expensive I actually don't use it (haven't done for 2 years) as I have economy 7 and a log burner works out cheaper to heat the house with logs and the water at night time.

I do like having the gas option there as a back-up but in reality I could probably do away with it, meaning no metal service pipes entering the house.

It would still need it to be capped correctly by a gas safe person, and like you say with lock-down. However I am in no rush it can wait till after, whenever that may be

 

[pc1966]

It might be worth asking a gas safe person if they could install an isolation section so you can keep the gas but not the bonding.

If you search for "Insulation inserts in metallic gas service pipes to consumers' premises" you should find an IET article on this sort of thing (pasting links to the IET site seem to get borked on this forum).

 

[marcuswareham]

MyEnergi Zappi would be the product for just this.

zappi EV Charger | 7kW & 22kW Home charger | myenergi

Fast charge your electric vehicle at home or work using cheaper and greener energy, with the original eco smart zappi EV charger. Made in Britain.

myenergi.com

Sorry I missed your replay,

Just had a look at this product it would appear to me that this device instead of monitoring the voltage. It uses a sensing coil round the earth conductor and once it detects a few 10s of mA it disconnects line, N and PE , correct?

Thanks Marcus

 

[Lister1987]

Sorry I missed your replay,

Just had a look at this product it would appear to me that this device instead of monitoring the voltage. It uses a sensing coil round the earth conductor and once it detects a few 10s of mA it disconnects line, N and PE , correct?

Thanks Marcus

It has inbuilt RCD protection and uses the current clamp to monitor overall load on incoming supply and lowers/increases its power consumption during time of high/low demand, if I'm remembering correctly it monitors current instead of voltage and being the only one (apparently) to work on this manner it will isolate correctly in the case of a broken neutral, whereas others won't

Of course rereading your post your just after sockets, not an EV Charger, my bad.

 

[marcuswareham]

If there is any simple way to TT supply the whole house and car port then all of the PME risk problems go away in one step.

I would try to ascertain if the service pipe work is bonded to the PME of neighbours first as that would negate any TT benefits. Some gas pipes now have insulated sections for this reason, and often the gas main is plastic even if the pipework in to the home is metal, so you might be OK there. Otherwise the trouble of sorting gas pipes is way too much and unlikely to be done during lock-down as not essential work!

Looking at the gas bottle store, It will be very easy to disconnect earth links between gas pipes to the other house and the separation between the pipes is around 1.2m. the gas bottles themself cannot easily touch the others and they are also connected via rubber hoses. Will this be enough separation in the ground, I could do a resistance test between the gas pipes for the other houses.

If I do convert to TT, what tests would I need to do in addition, I am thinking measure Ze, earth rod impedance, test all RCD's disconnection times and that it? , and all of the bonding already in place for PME will be oversized but that's no problem

It looks as if I should be able to get earth rod resistance down to around 15-20ohm using 2 rods and the gas pipe

Also I do minor works certs for the work I do on my house, would a minor works certs for changing to TT do, and if so the format of a minor work cert doesn't lend its self to this, so what documentation could be better instead