Total Heating Total Control wiring issue

[Ray Shields]

My flat has an old SSE THTC setup. Basically one meter (on the right) feeds the top CU (both are metal) which covers all the sockets, lights etc. 

The Radio Teleswitch on the left supplies permenant power to the water heater and 4 convectors. There is also a permenant supply to a Heater Boost button for heating up hot water quicker. 

 

The Teleswitch also tops up at various times 3 storage heaters. 

 

So, 4 different live feeds. 

 

I recently had an EICR done, it has been given a C2 (521.5.1) because there is one neutral which goes through from the meter box onto a Henley block and then 4 feeds into the CU in the top. Thus live and neutrals not going through the same holes, classed as a C2 as the lives come in through the rear of the CUs. 

 

To sort this I suspect the Henley block will have to go back to the meter box and the 4 neutrals then follow the live cables in through the rear of the CU. Not sure there's enough hole space to allow this. 

 

My question, though, is that this is an original installation from about 25 years ago, it must have passed its initial installation certification. The last EICR I had done was in 2017, and it did not fail on this, not even a comment. 

 

When did this requirement first appear, could it be that this was legal at the time but not now (if so this is a C3, not to current spec). Could the electrician feed one neutral into the lower CU and daisy chain it across the 3 MCB/RCD? If so it would mean only one new additional neutral fed from meter box rather than 3.

 

[ProDave]

Picture please.  I am struggling to understand why one through the side and one the rear matters.

 

Is it a case of the hole the cables go through is too big and not the correct IP rating?

[Mattg4321]

Eddy currents maybe?

 

That being the case though a C3 seems more reasonable if no ill effects are observed and it’s been in service for that long. 

[ProDave]

I would be asking him what guidance note says it is a C2. i.e. asking hum to justify that.

[Mattg4321]

As far as I know it’s not mentioned in BPG4. 
 

Might be hard to change someone’s mind on this though as it’s ultimately the inspectors opinion. 
 

https://www.electricalsafetyfirst.org.uk/media/2depcuen/best-practice-guide-4-issue-6.pdf

[Ray Shields]

Sorry, I attached photos or so I thought. Meter cupboard in outside of building 

[Ray Shields]

2 consumer units in side, note the neutrals going in top, the lives go in the rear. Top CU is for normal rate bottom one for all heating and timed supplies

[Ray Shields]

[Ray Shields]

On 07/04/2024 at 19:13, ProDave said:

Picture please.  I am struggling to understand why one through the side and one the rear matters.

 

Is it a case of the hole the cables go through is too big and not the correct IP rating?

Pics posted, sorry thought I had. There is just one neutral coming through, distributed via Henley block, suppose they couldn't fit 4 live and 4 neutral meter tails (so just put through 4 live and 1 neutral.) through the brick wall hole from the meter box to inside CU. Lives come in the rear. 

 

 

[Ray Shields]

The inspector quoted 521.5.1 that states for a metal box live and neutral must pass through the same hole to stop eddy currents causing heat. So basically he says each neutral must come through each corresponding live hole in the rear. 

 

 

[Ray Shields]

14 hours ago, Mattg4321 said:

Eddy currents maybe?

 

That being the case though a C3 seems more reasonable if no ill effects are observed and it’s been in service for that long. 

The EICR states the inspector noted overheating. I've looked, I can see none.

[Mattg4321]

He’s correct in that it’s against the regulations. However in practice it’s unlikely to cause a problem at a domestic level with relatively low currents. 
 

You’ve also got issues there with basic insulation of the meter tails being visible and cable thus not mechanically protected. The meter tails are not properly supported and also quite likely IP rating to top surface of consumer unit  not to IP4X. 
 

Nothing major, and all could be argued C2 or C3 depending on exact circumstances. It might just be worth getting someone to tidy them up - doesn’t have to be original inspector, you just append the invoice\certificate for the work to the original EICR to show the remedials have been carried out. 

[ProDave]

The fix to that, is power down, remove the tails, put a hacksaw cut between each of the holes, replace and re connect cables.

 

But if there is no actual evidence of heating, and it has been like that for probably 30 or more years, I would challenge the tester to justify a C2 rather than a C3

 

Why did you have the EICR?  If it is just for information, you are not obliged to have it fixed.  Only if it is something like a rental do you have to have a satisfactory EICR/

[Ray Shields]

On 09/04/2024 at 09:00, ProDave said:

The fix to that, is power down, remove the tails, put a hacksaw cut between each of the holes, replace and re connect cables.

 

But if there is no actual evidence of heating, and it has been like that for probably 30 or more years, I would challenge the tester to justify a C2 rather than a C3

 

Why did you have the EICR?  If it is just for information, you are not obliged to have it fixed.  Only if it is something like a rental do you have to have a satisfactory EICR/

Yes it's a rental so can't have any C2. I had 6 C2s, I agree with them all apart from the neutral one which I feel is a C3. 

 

Does the hacksaw slot work when they are all neutrals? I thought it was if one was live, one was neutral. Thanks.

[ProDave]

You want a hacksaw cut between L and N  Can you not get the rogue cable that enters in the back re routed to enter the top like the rest, thena hacksaw cut between all the holes will solve the problem.

[Ray Shields]

On 11/04/2024 at 08:43, ProDave said:

You want a hacksaw cut between L and N  Can you not get the rogue cable that enters in the back re routed to enter the top like the rest, thena hacksaw cut between all the holes will solve the problem.

One box has 3 lives going in, the other has 1, if the lives were long enough I would consider putting them in one of those 32mm glands that allow l, n & e tails in, which would solve the problem. But they aren't. 

 

Realistically, im going to fix the other outstanding C2s and then go back and argue the case for this one being a C3. If that doesn't work im cheaper getting one of the previous EICR companies to do a new one (and if they try arguing it I can show that they passed it previously). EICR costs, £175 ex vat here. 

[ProDave]

You (or at least your electrician) can replace the meter tails with longer ones.

 

However another issue coming down the tracks is the future of THTC.  It is an old SSE system with the USP of offering cheap rate 24/7 for heating appliances.  I hear nothing but complaints now as not many suppliers other than SSE will take it on, and it has become expensive.

 

A long term future perhaps is converting to standard E7 or E10.  While it is possible to do that just by reconfiguring the existing consumer units, it might be time if doing that to replace with new CU's one for peak one for off peak all correctly wired so all the issues go away.

[Ray Shields]

1 minute ago, ProDave said:

You (or at least your electrician) can replace the meter tails with longer ones.

 

However another issue coming down the tracks is the future of THTC.  It is an old SSE system with the USP of offering cheap rate 24/7 for heating appliances.  I hear nothing but complaints now as not many suppliers other than SSE will take it on, and it has become expensive.

 

A long term future perhaps is converting to standard E7 or E10.  While it is possible to do that just by reconfiguring the existing consumer units, it might be time if doing that to replace with new CU's one for peak one for off peak all correctly wired so all the issues go away.

Yes, I've thought about that, and the upcoming switch off of the long wave transmitters to operate the Teleswitch. I have a Tenant moving in on 2 weeks time, so I don't think I'll have enough time to sort it all this time round. 

 

Thanks for your advice. 

[Crofter]

We have a house on THTC and we've had to move to OVO now.

No word yet on the tariff coming to an end, but I've heard rumours from other parts of Scotland.

 

If they do end it, my problem is that simply switching to E7/E10/standard won't be itself be an option. My heaters are controlled by the time switch, they do not have any timers they I can control.

 

It's not going to be very fair on little old ladies with the same type of installation as me to expect to have to get a sparky to install the necessary timers/controls, out of their own pocket. Hopefully there will be some sort of grant to cover this.

[ProDave]

The suppliers make it hard for themselves (and us)

 

The only thing that separates THTC from E7/10 is the second meter that meters the 24/7 cheap rate.

 

In it's simplest form, to convert from THCT to E7 they just need to remove the second meter, leaving the existing dual rate meter and time switch, and connect the feed to the heating circuits to the normal rate feed with a henley block.

 

An electrician can't do that as we are not allowed to touch the metering.  I don't know why the suppliers cannot just offer that as a simple option.

 

That still leaves the radio teleswitch that will need replacing some day whether or not you change to E7 or stay with THCT, that is a problem yet to solve.

 

As I understand it, in the  absence of a radio signal it becomes a dumb timer so on / off periods may creep a litte depending how accurate it is.  Not sure how it handles a power cut.  As a temporary measure they could always fit a mechanical timer, remember the old Sangmo Weston timers that were clockwork with spring backup for a power cut?