New Consumer Unit

[uksparks]

Trainee question! Would I be right in saying that although it's TN-C-S it might not necessarily be PME?

True, but I think if you ring WPD they will say all TNC-S is now PME, I just call it the same, because it generally is as far as I am concerned.

 

[Resu]

True, but I think if you ring WPD they will say all TNC-S is now PME, I just call it the same, because it generally is as far as I am concerned.

Hey, I don't doubt it mate, was just an observation!

 

[Leesparkykent]

Unfortunately this is a mid terrace, quite an old property, probably 1930 I think, no access either side due to neighboring houses.

Its kind of a non starter, plus the bathroom and kitchen are both downstairs at the back of the house which is quite deep front to back and no water at all in the rest of the house, so would literally have to go from front to back and probably trash half the house in the process.

View attachment 27753

could well still be TNS even though it looks like TNC-S.

 

[davesparks]

Your average 1930's built house is going to have suspended floors downstairs and T&G floorboards both up and downstairs, so spring a few floorboards and run a 10mm bond to where you need it.

This is of course assuming you have already confirmed that bonding is actually required in the first place?

There are a lot of 1970/80's terraces and wimpey homes around here which follow the basic layout of gas and electricity by the front door and water main under the sink at the rear of the house with 6mm main bonds. The water main is however a black plastic pipe and rarely actually requires a main bond in the first place so I am normally perfectly happy leaving it as it is.

 

[7029 dave]

Looked at the pic, IMO if the 6mm bond is mech okay and no thermal damage leave it. Measure it as well for piece of mind. (you know the value you are looking for.)

 

[davesparks]

Trainee question! Would I be right in saying that although it's TN-C-S it might not necessarily be PME?

You are right in saying that yes, all PME supplies are TNCS but not all TNCS supplies are PME. for a start there is a system called PNB (protective neutral bonding) which has just one N-E connection via an earth electrode wheras PME has multiple earth electrodes.

True, but I think if you ring WPD they will say all TNC-S is now PME, I just call it the same, because it generally is as far as I am concerned.

That is a brilliant answer to give to a trainee asking a reasonable question!

 

[TJ Anderson]

You are right in saying that yes, all PME supplies are TNCS but not all TNCS supplies are PME. for a start there is a system called PNB (protective neutral bonding) which has just one N-E connection via an earth electrode wheras PME has multiple earth electrodes.

That is a brilliant answer to give to a trainee asking a reasonable question!

Is the earthing requirement different for PNB & PME? I cant see that it would be.

 

[HandySparks]

I have a consumer unit to change, the earth on the gas is easy enough but the water is in 6mm and literally the other end of the house and would be a nightmare running in a new cable

Just to add, it is green and yellow, so not like its just green.

Your average 1930's built house is going to have suspended floors downstairs and T&G floorboards both up and downstairs, so spring a few floorboards and run a 10mm bond to where you need it.

This is of course assuming you have already confirmed that bonding is actually required in the first place?

As davesparks says, see what the ground floor construction is. If suspended floor, then it may be easy. In fact, since the existing cable isn't the original you might find that you can use it as a pull through.

 

[davesparks]

Is the earthing requirement different for PNB & PME? I cant see that it would be.

No the earthing and bonding requirements are the same.

 

[uksparks]

Yes it could be split in the head, without measuring it I dont know.

The floor in the front room is suspended but the middle room and kitchen appears to be solid unfortunately.

yes I accept its not a very accurate answer to give a trainee.

 

[Leesparkykent]

Yes it could be split in the head, without measuring it I dont know.

The floor in the front room is suspended but the middle room and kitchen appears to be solid unfortunately.

yes I accept its not a very accurate answer to give a trainee.

Thats exactly how most of the older terraced houses round my way are as well. How will you test it to confirm it's TNS or TNC-S?

 

[davesparks]

Thats exactly how most of the older terraced houses round my way are as well. How will you test it to confirm it's TNS or TNC-S?

As a general rule :
TNCS - PEFC = PSCC
TNS - PSCC > PEFC

 

[spark 68]

How will you test it to confirm it's TNS or TNC-S?

By comparing Ze and Zp-N, if the readings are identical then it will be TNC-S, this is because of the CNE link in the head and the PEN conductor are common to the N and E.

 

[HandySparks]

By comparing Ze and Zp-N, if the readings are identical then it will be TNC-S, this is because of the CNE link in the head and the PEN conductor are common to the N and E.

Anyone tried checking for TN-C-S / TN-S by measuring the resistance between the incoming neutral at the first accessible point (assuming reasonably close) and the earthing terminal on the head?

Main switches all off, so no current flow and check for any voltage, just in case.

I would have thought that this might be a more reliable and direct way of telling? Clearly if there's any significant voltage or resistance between these points, then there's no local connection between the two.

 

[spark 68]

Anyone tried checking for TN-C-S / TN-S by measuring the resistance between the incoming neutral at the first accessible point (assuming reasonably close) and the earthing terminal on the head?

Main switches all off, so no current flow and check for any voltage, just in case.

I would have thought that this might be a more reliable and direct way of telling? Clearly if there's any significant voltage or resistance between these points, then there's no local connection between the two.

Well I check them at the same time, obviously because I am checking Ze the main switch is off anyway, and in domestic the tails are usually fairly short and I am testing from the live side of the mains switch, and with only a short run for the 16mm EC it makes no practical difference.

Bearing in mind this test (for TNC-S v TNS) is only really necessary on the odd occasion where it could be an either/or situation