BS7671 test and internal electric heating

[HappyHippyDad]

Right, I think I've nearly got to the bottom of this with the electrician now.

When I asked him about the various differences between the 2008 report and his, he noted the following:

- The 2008 report showed a very low (almost non-existent) for insulation resistance on the heating circuit - which would seem to imply that the other electrician also struggled to get a meaningful reading (or any reading at all) out of that circuit;

- The 2008 report did however show what appears to be suitable Zs readings for the heating circuit and the off-peak water, something which my current electrician hasn't able to manage. He's unsure how the previous electrician would have got such a reading given the lack of power and the switches/timers (ie isolation) in the circuit;

- I also queried why he hadn't tested the continuity (Ring final circuit continuity in respect of the "sockets" circuit, and R1+R2 continuity for all circuits) in his report, when the previous electrician had. His response was "There’s no need to do continuity testing on a periodic. If the testing of Zs and Insulation Resistance gives good results, then that really proves a safe circuit which is the aim of the exercise. BS7671 merely states to undertake ‘appropriate tests’. If another sparky chooses to do continuity, that’s up to him but it’s always down to discretion and appropriateness."

So his stance on the heating circuit seems to match up with the outcome of the 2008 report.

I'd be grateful if any of you have any comments on the 2nd point (regarding the inability to test Zs) and 3rd point (whether continuity testing is/isn't part of a periodic test)!!

With regards your first point, an insulation resistance reading is a dead test (conducted with power off) so your electrician could have done this test, I am unsure if he did or not? Also, a low insulation resistance result does not mean that he had difficulties obtaining the result, it means he tested it and that was the result he got. A result of 1MΩ or greater is acceptable, and a result of below 1MΩ means that circuit requires attention.

With regards your second point (the Zs readings) as Richard has said the original electrician may have just calculated this from looking at the Ze result and adding it to the R1+R2 result (so it could be obtained with the power to the heating circuit off). You could perhaps look at these 2 results (Ze and (R1+R2)) and if added together equal 'exactly' the result he has put for Zs then he 'may' have just calculated the Zs (unless coincidentally that was the measured Zs, but unlikely). Ze may be written as 'Zs at DB' on the report that you have.

So, with the power to the heating off your electrician would not be able to carry an actual 'measurement' of the Zs, but he could carry out an R1+R2 of this circuit and add it to the Ze (to obtain a calculated Zs).

Again, as Richard has said not all electricians will carry out a R1+R2 on a report if they get a satisfactory Zs so i dont think your electrician should be penalised for this, but an R1+R2 on the heating circuit would have been necessary as no Zs was obtained.

Lastly, it's very difficult to give 100% guaranteed advice without seeing the installation.

It would be interesting to know how long the electrician was there for and how much he charged?

 

[Risteard]

To get this into perspective, it is not a "periodic test". It is a periodic inspection. Inspection precedes testing, and is the more important aspect. (Many problems will not be located through testing.) The testing merely supplements the testing.

Also, I presume happyhippydad did not mean to suggest that an insulation reading of 1 Ohm would be acceptable!

 

[Leesparkykent]

To get this into perspective, it is not a "periodic test". It is a periodic inspection. Inspection precedes testing, and is the more important aspect. (Many problems will not be located through testing.) The testing merely supplements the testing.

Also, I presume happyhippydad did not mean to suggest that an insulation reading of 1 Ohm would be acceptable!

??????

 

[HappyHippyDad]

To get this into perspective, it is not a "periodic test". It is a periodic inspection. Inspection precedes testing, and is the more important aspect. (Many problems will not be located through testing.) The testing merely supplements the testing.

Also, I presume happyhippydad did not mean to suggest that an insulation reading of 1 Ohm would be acceptable!

Thanks for pointing that out Risteard! How embarrassing! Have amended.

 

[Risteard]

??????

LOL. I meant the testing merely supplements the inspection!

 

[GEOFF S]

The central heating system will fall outside the scope of BS7671 try BS EN 14336:2004. The fixed wiring upto the controls/? will be under BS7671

Cheers

 

[Leesparkykent]

The central heating system will fall outside the scope of BS7671 try BS EN 14336:2004. The fixed wiring upto the controls/? will be under BS7671

Cheers

It's not a water based heating system.

 

[GEOFF S]

It's not a water based heating system.

Thanks Lee, just saw central heating. That said, this productt will have its own product standard to which it needs to de designed, installed, commisioned and tested.

Cheers

 

[Soup]

Thanks everyone for your comments on this. It's quite confusing as a layman with no electrical knowledge/training so I'm trying to get up to speed here!

With regards your first point, an insulation resistance reading is a dead test (conducted with power off) so your electrician could have done this test, I am unsure if he did or not? Also, a low insulation resistance result does not mean that he had difficulties obtaining the result, it means he tested it and that was the result he got. A result of 1MΩ or greater is acceptable, and a result of below 1MΩ means that circuit requires attention.

It would appear the electrician who did my recent inspection has not done this test on the heating circuit - he has left all readings blank on the heating circuit and stated on the test sheet "unable to test due to timers in the circuit".

On the 2008 report, the results the electrician got on the heating circuit were 0.07, 0.08 and 0.07 for phase/neutral, phase/earth and neutral/earth respectively (for insulation resistance). R1+R2 was 0.25. Zs figure was 0.47.

As these figures appear to be below 1MΩ, what "attention" would this circuit would require in your opinion?

With regards your second point (the Zs readings) as Richard has said the original electrician may have just calculated this from looking at the Ze result and adding it to the R1+R2 result (so it could be obtained with the power to the heating circuit off). You could perhaps look at these 2 results (Ze and (R1+R2)) and if added together equal 'exactly' the result he has put for Zs then he 'may' have just calculated the Zs (unless coincidentally that was the measured Zs, but unlikely). Ze may be written as 'Zs at DB' on the report that you have.

So, with the power to the heating off your electrician would not be able to carry an actual 'measurement' of the Zs, but he could carry out an R1+R2 of this circuit and add it to the Ze (to obtain a calculated Zs).

Again, as Richard has said not all electricians will carry out a R1+R2 on a report if they get a satisfactory Zs so i dont think your electrician should be penalised for this, but an R1+R2 on the heating circuit would have been necessary as no Zs was obtained.

I can't find the Ze figure on either report, either shown as Ze or "Zs at DB". Does Ze relate to the total of the insulation resistance readings?

If so, that might work for the heating circuit - as per my point above, on the 2008 report I have readings of 0.25 (R1+R2) plus 0.07+0.08+0.07 (sum of insulation resistance readings) = 0.47 - which matches to the Zs reading on the report.

However, this calculation doesn't seem to work for the off-peak immersion circuit reading on the 2008 report - this has 0.11 R1+R2, then >500 on all 3 insulation readings. Zs total on this circuit per the 2008 report is 0.30.

It would be interesting to know how long the electrician was there for and how much he charged?

He charged me £90 (no VAT as not registered). Based on his hourly rate for other non-electrical work, that would appear to be 2 hours he spent doing the testing and completing the report/testing details on the summary sheets he gave me. This seems cheap (like the budgie) in comparison with what I spent on the 2008 report and the other quote I had for the work recently.

 

[Soup]

UPDATE TO THE ABOVE POST:

I've found the Ze readings on the reports!

2015 report (current report) = 0.04Ω

2008 report (old report) = 0.23Ω

So... looking at the 2008 report.... 0.25 R1+R2 +0.23 Ze = 0.48 (calculated Zs). Zs per the report = 0.47. So virtually exactly the same, like you guys said. Although that might still indicate the 2008 electrician managed to get a "normal" Zs reading of some sort as the Zs figures aren't identical.

So, I think I will go back and ask the current electrician if there was a reason why he didn't use the alternative calculated Zs (ie do an R1+R2 reading) in the absence of a standard Zs reading.

Is there any issue with the differences between the two Ze readings? (the 2015 Ze reading seems quite low comparatively with the 2008 Ze reading)

This does also still leave the question about the low readings on the heating circuit insulation resistance (less than 1MΩ) so I'd be grateful if you would let me know "attention" this circuit might need, in your opinion?

Thanks guys, your help is much appreciated.