Amd3 Transitional Period

[JohnW2]

The BYB (aka Amd 3 of BS7671:2008) is published on Monday, and has an 'effective date' of 1st July. That clearly means that, as of 1st July, all new installations and new work will be required to be compliant with Amd3, but what do folk do in the intervening transitional period? It would seem to make sense for all work undertaken during that period to be Amd3-compliant, but what about EICRs during that period - would one mention (or even code) things which were currently compliant but which would not be compliant with Amd3?

In passing, I wonder how many installations have final circuits with Zs figures which are sufficiently marginal that, although currently compliant, will not be compliant under Amd3 (whether they have decided upon Cmin=0.95 or 0.94) ???

Kind Regards, John

 

[PrenticeBoyofDerry]

I am continuing using the amd 2 version until I get my head around amd 3 and the prices of the publications come down, so I can study them in better detail.

 

[JohnW2]

I am continuing using the amd 2 version until I get my head around amd 3 and the prices of the publications come down, so I can study them in better detail.

That's a pretty pragmatic answer! I don't think you should hold your breath too much in waiting for the price to become sensible, at least from mainline suppliers. Two years down the road, Amazon are currently still selling the BGB (Amd1) for £60.45, as compared with £76.50 for BYB.

I don't think that there is any doubt that the wide-ranging changes in 'maximum Zs' figures (and associated PEFC/PSCC etc.) are going to be the changes that have most impact, whilst the removal of blanket 'compulsion to ('blindly') obey MIs' will also be welcomed by some!

Kind Regards, John

 

[EFLImpudence]

In passing, I wonder how many installations have final circuits with Zs figures which are sufficiently marginal that, although currently compliant, will not be compliant under Amd3 (whether they have decided upon Cmin=0.95 or 0.94) ???

I would say very few, if any, in the usual domestic situation...

and even less if actual conductor temperatures were used.

 

[JohnW2]

In passing, I wonder how many installations have final circuits with Zs figures which are sufficiently marginal that, although currently compliant, will not be compliant under Amd3 (whether they have decided upon Cmin=0.95 or 0.94) ???

I would say very few, if any, in the usual domestic situation...

Thanks. That's what I rather presumed. If there are issues, I would expect that they would be most likely to be seen in high current (e.g. shower) circuits in TN-S installations. When the 'maximum Zs' falls below, say, 1Ω, the Ze may possibly be sufficiently high as to not leave much for the R1+R2 of the final circuit. I would think that some of the more marginal of 'outhouse supplies' may also raise issues.

...and even less if actual conductor temperatures were used.

That doesn't seem totally straightforward. Presumably there is a requirement that disconnection times be satisfied even if a 'full-blown fault' arises when a circuit is already fully loaded, hence 'hot'?

Whatever, if (despite being unlikely) you did encounter next week a Zs which was OK per BGB, but not per BYB, would you mention (or even code) it on an EICR? (presumably you would have to once we get to July?)?

Kind Regards, John

 

[EFLImpudence]

...and even less if actual conductor temperatures were used.

That doesn't seem totally straightforward. Presumably there is a requirement that disconnection times be satisfied even if a 'full-blown fault' arises when a circuit is already fully loaded, hence 'hot'?

That is my point. How often is a conductor actually able to be fully loaded?

Whatever, if (despite being unlikely) you did encounter next week a Zs which was OK per BGB, but not per BYB, would you mention (or even code) it on an EICR? (presumably you would have to once we get to July?)?

Until July, you could merely note it, I suppose. After that does it become danger present or potentially dangerous?
It still won't be retrospective so, either way, only code 3.

Will/is there be the usual "planned before" allowance?

 

[JohnW2]

...and even less if actual conductor temperatures were used.

That doesn't seem totally straightforward. Presumably there is a requirement that disconnection times be satisfied even if a 'full-blown fault' arises when a circuit is already fully loaded, hence 'hot'?

That is my point. How often is a conductor actually able to be fully loaded?

Obviously not very often - at least for most types of circuit (showers may be an exception, and some dedicated heating and immersion circuits quite close). However, I could equally well ask you how often the supply to an installation is going to be as low as 218.5V (or 216.2V) - yet JPEL have now clearly decided that disconnection times need to be satisfied in such a rare situation.

Until July, you could merely note it, I suppose.

Indeed - but I'm asking whether 'you' (or electricians in general) would feel obliged to do even that (pre-July)?

After that does it become danger present or potentially dangerous? It still won't be retrospective so, either way, only code 3.

Indeed. Of course, for those households whose supply is usually <230V, it represents the difference between satisfying and not satisfying disconnection times - which I suppose some might argue impacts on 'danger'!

Will/is there be the usual "planned before" allowance?

I don't know - I suppose that's one of the questions I was asking/pondering. There probably is such a provision but, given the 6 months' 'notice' implicit in the system, it has always struck me as being a fairly generous provision!

Kind Regards, John

 

[EFLImpudence]

Obviously not very often - at least for most types of circuit (showers may be an exception, and some dedicated heating and immersion circuits quite close). However, I could equally well ask you how often the supply to an installation is going to be as low as 218.5V (or 216.2V) -

I do not think you can equally ask me.
I am replying to your query about the new lower values of Zs which I think will have no effect.
I disagree about immersions; they are normally wired with 2.5mm² out of reverence for 3036s and even showers rarely match the cable CCC.

yet JPEL have now clearly decided that disconnection times need to be satisfied in such a rare situation.

They do. It will probably affect industry but not domestic.

Indeed - but I'm asking whether 'you' (or electricians in general) would feel obliged to do even that (pre-July)?

Not obliged but it would seem prudent.
Don't forget that I don't think it will happen.

 

[JohnW2]

Obviously not very often - at least for most types of circuit (showers may be an exception, and some dedicated heating and immersion circuits quite close). However, I could equally well ask you how often the supply to an installation is going to be as low as 218.5V (or 216.2V) -

I do not think you can equally ask me. I am replying to your query about the new lower values of Zs which I think will have no effect.

Fair enough. However, I can 'equally ask' - if not equally ask you! I was actually responding to your comment about conductor temperature - agreeing that it is unlikley that a circuit will ever be anything like 'fully loaded', but suggesting that such an unlikely scenario may not be any more unlikley that a supply voltage of 218.5V.

I disagree about immersions; they are normally wired with 2.5mm² out of reverence for 3036s and even showers rarely match the cable CCC.

Agreed, but they will still run at above ambient temperature.

yet JPEL have now clearly decided that disconnection times need to be satisfied in such a rare situation.

They do. It will probably affect industry but not domestic.

You're probably right - although, ironically, I suspect that it's even less likely that that industrial installations will have very low supply voltages!

Indeed - but I'm asking whether 'you' (or electricians in general) would feel obliged to do even that (pre-July)?

Not obliged but it would seem prudent. Don't forget that I don't think it will happen.

Fair enough. I suppose that if I wanted to be mischievous, I might suggest that if you are so confident that domestic Zs never gets so close to the (current) 'permitted maximum' that a 5% or 6% drop in that maximum won't make any difference, then there is probably no need for you to measure Zs in domestic situations

Kind Regards, John

 

[EFLImpudence]

Fair enough. However, I can 'equally ask' - if not equally ask you! I was actually responding to your comment about conductor temperature -

Ambient, yes; maximum, doubtful - so my point is that an adjustment of 1.2 being necessary at the same time as the voltage drops to minimum is extremely unlikely for most circuits and impossible for some.
If it is likely then it can be designed.

agreeing that it is unlikley that a circuit will ever be anything like 'fully loaded', but suggesting that such an unlikely scenario may not be any more unlikley that a supply voltage of 218.5V.

Therefore both at the same time as a fault - ?

You're probably right - although, ironically, I suspect that it's even less likely that that industrial installations will have very low supply voltages!

That may be so but the powers that be have decided that we must cater for it.
Are you suggesting they are making work for themselves?

Fair enough. I suppose that if I wanted to be mischievous, I might suggest that if you are so confident that domestic Zs never gets so close to the (current) 'permitted maximum' that a 5% or 6% drop in that maximum won't make any difference, then there is probably no need for you to measure Zs in domestic situations

Mischievous ?
I suppose but it is a check; we cannot tell by looking at it and we have to record numbers.

 

[JohnW2]

Ambient, yes; maximum, doubtful - so my point is that an adjustment of 1.2 being necessary at the same time as the voltage drops to minimum is extremely unlikely for most circuits and impossible for some.

We're not talking about a situation in which "the voltage drops to a minimum" - but, rather, of an installation in which the supply voltage usually/always is close to the minimum permitted.

agreeing that it is unlikley that a circuit will ever be anything like 'fully loaded', but suggesting that such an unlikely scenario may not be any more unlikley that a supply voltage of 218.5V.

Therefore both at the same time as a fault - ?

As above, the two things are independent. It is no less likely that the need for temperature adjustment will arise when the the supply voltage is 220V than when it is 250V (although it is less important in the latter case). However, we are agreed that both situations are rare.

You're probably right - although, ironically, I suspect that it's even less likely that that industrial installations will have very low supply voltages!

That may be so but the powers that be have decided that we must cater for it. Are you suggesting they are making work for themselves?

Not at all. I have always said that it seemed very surprising ('wrong'?) that the prescribed way of determining whether Zs is low enough means that the specified disconnection times will not be achieved in an installation whose supply voltage is less than 230V. The "powers that be" have now (almost or completely - wait for Monday!) addressed that, but they have not singled out industrial installations as being the only ones that will be affected - it is you who (possibly correctly) have done that.

Fair enough. I suppose that if I wanted to be mischievous, I might suggest that if you are so confident that domestic Zs never gets so close to the (current) 'permitted maximum' that a 5% or 6% drop in that maximum won't make any difference, then there is probably no need for you to measure Zs in domestic situations

Mischievous ? I suppose but it is a check; we cannot tell by looking at it and we have to record numbers.

Quite. Your acknowledgement of the need to 'check' presumably means that you do not actually regard it as a foregone conclusion that Zs in domestic final circuits will never be close to (or even above) the (pre-Amd3) 'maximum'.

Kind Regards, John

 

[ericmark]

411.3.2.2 is the main regulation in the original BS7671:2008 not exceeding 32A "NOTE 2: Where compliance with this regulation is provided by an RCD" clearly states an RCD can be used as one has to with a TT supply.

So in the main using a RCD means one does not have to have a Zs under 1.44&#937; for a B32 MCB. The question is do you need a line - neutral loop impedance of under 1.44&#937;?

Clearly 1.44&#937; with a ring final line - neutral reading would mean an unacceptable volt drop but as to if that presents a danger is another question.

Code C3 (Improvement recommended) really does need some further notes with the old compiles with previous edition it was easy as new editions were released then old 4 became 3 giving the owner some time to upgrade but to recommend an improvement to me you must say why.

So C3 no RCD protection on socket outlets without this protection any additions to the circuit will be expensive. Is fair comment but simply C3 no RCD is not really acceptable.

So C3 Zs exceeds 1.28&#937; unless corrected (What?).

How can you tell a home owner his house was safe in 2014 but without any change to his house in 2015 it's no longer safe because the IET made a mistake with their recommendation. The question is then will the IET pay for upgrade?

So maybe the answer should be the DNO have reduced the voltage supplied to your house. Reply is will the DNO pay for upgrade?

So I will rephrase the question if you are going to issue a C3 because the Zs limit has been reduced what would you tell the home owner in layman's terms is the reason for failing it?

We had the discussion on volt drop before and in the main any reading of more than 1.28&#937; as Zs on a final ring with a TN-C-S supply means it also likely does not comply with volt drop. But that means working out volt drop and stating volt drop exceeds 5% and to be frank I looked at errors and it may work out using pure maths but our meters would need to be super accurate to be sure it was exceeded.

This is of course the same for the 1.44 or 1.28 reading how accurate is the earth loop impedance meter? The meter reads the difference in on load and off load voltage and once any loads are added or subtracted while being measured it will give a wrong answer this includes any load from that supply transformer so although it may record to 2 decimal places to condemn an installation one would need to measure a few times of course allowing meter to cool between each test.

So in real terms unless well over the permitted value one can't really give it a coding. So I would say for a ring final over 1.5&#937; yes report under that then I would not enter as a code.

 

[ban-all-sheds]

How often is a conductor actually able to be fully loaded?

Is there any published data on how long a cable takes to reach 70° when fully loaded?

 

[EFLImpudence]

We're not talking about a situation in which "the voltage drops to a minimum" - but, rather, of an installation in which the supply voltage usually/always is close to the minimum permitted.

Why or what's the difference?

but they have not singled out industrial installations as being the only ones that will be affected - it is you who (possibly correctly) have done that.

Well, in a way. It's just that long distances will have to account for it.

Quite. Your acknowledgement of the need to 'check' presumably means that you do not actually regard it as a foregone conclusion that Zs in domestic final circuits will never be close to (or even above) the (pre-Amd3) 'maximum'.

It's not a question of checking to see if near the maximum but to see if it is connected and whilst doing so the value will appear and a ring with a Zs of 0.4&#937; needs little further consideration.

 

[JohnW2]

411.3.2.2 is the main regulation in the original BS7671:2008 not exceeding 32A "NOTE 2: Where compliance with this regulation is provided by an RCD" clearly states an RCD can be used as one has to with a TT supply.

That is true, but as we've often discussed, 415.1.2 says "The use of RCDs is not recognised as a sole means of protection and does not obviate the need to apply one of the protective measures specified in Sections 411 to 414". I think that (despite the note to Table 41.1 which you quote) most people interpret this as meaning that, unless it is unavoidable (i.e. in TT systems), one should not rely on an RCD to achieve the required disconnection times but should achieve that per 411 (i.e. with an OPD).

So in the main using a RCD means one does not have to have a Zs under 1.44&#937; for a B32 MCB. ...

As above, I don't think that's how most people interpret the above regs, particularly 415.1.2 - but maybe I'm wrong.

....The question is do you need a line - neutral loop impedance of under 1.44&#937;?

If (as I presume is the case) one wants disconnection by the magnetic trip of an MCB (i.e. in less than about 10 seconds), then one clearly has no choice but to impose that requirement for L-N loop impedance, even in a TT installation.

Clearly 1.44&#937; with a ring final line - neutral reading would mean an unacceptable volt drop but as to if that presents a danger is another question.

As above, an L-N loop impedance >1.44&#937; (at 230V) would/could result in disconnection in response to a 'dead short' taking longer than 10 secs - I would think that could be said to 'present a danger'.

How can you tell a home owner his house was safe in 2014 but without any change to his house in 2015 it's no longer safe because the IET made a mistake with their recommendation.

'Safe' obviously comes in shades of grey, and opinions (both official and general) about what degree of 'safeness' is required vary,both between individuals/organisations and with time. I could easily rephrase your question by asking "How can you tell a driver in Scotland that a level of alcohol in his blood which would have been regarded as 'acceptable' just 5 weeks ago is regarded as unacceptable ('unsafe' and illegal) today?".

So I will rephrase the question if you are going to issue a C3 because the Zs limit has been reduced what would you tell the home owner in layman's terms is the reason for failing it?

I think I would read to him my previous paragraph - adding that although his/her installation is obviously no less safe than it used to be, views about what level of safeness is required have changed. So many of the things which went on, and were accepted, when you and I were at school would today be condemned (and in many cases outlawed) as being 'unacceptably unsafe'!

So in real terms unless well over the permitted value one can't really give it a coding. So I would say for a ring final over 1.5&#937; yes report under that then I would not enter as a code.

If you're saying that simply because you don't trust the accuracy of your measurements, then it may be fair enough. However, if you were confident that the true Zs was >1.44&#937;, even if only slighly so, you really ought to 'report' it, shouldn't you?

Kind Regards, John