Advisory after new shower fitted

[ericmark]

EFLI is less than 2 OHMS

greater than 1.09 Ohms

These are the reverse of each other, is it greater or less, If less, then no problem, if greater, then may be a problem. To me, it would alert me to look at the line - neutral impedance, the line - earth is covered by the RCD, the line - neutral is not, a B40 MCB will in fullness of time trip at 40 amps, but that would take a long time, so as well as the thermal trip, it has a magnetic trip which is very fast, that with a B should trip at between 3 and 5 times the thermal setting, so 5 x 40 = 200 amps, so 230/200 = 1.15Ω add 5% for safety, and we have 1.09Ω maximum line - neutral impedance to ensure the trip will open in time.

But it is the line - neutral which is important to be below 1.09Ω as the line - earth is protected by the RCD, most testers display the line - neutral in amps, so 210 prospective short circuit amps or higher.

So with amps not below 210A, and with ohms not above 1.09Ω for the line - neutral but for line - earth with a 30 mA RCD it is 200Ω or below which is required. However, if at the consumer unit I was to measure 0.35Ω and at the shower I was to measure 3Ω it would flag up a fault. We can expect the line - neutral to be a little lower to the line - earth, as the neutral wire is thicker than the earth wire, but not by much, in the same way with a shower 4 meters from the consumer unit, would expect 0.38Ω. To get 1.09Ω with 10 mm² looking at around 100 meters or more. So even if within the limits, unexpected readings should trigger a red flag, as something wrong somewhere.

But 2Ω seems odd, if it was 1.99Ω, or 2.01Ω it would seem correct, but to measure bang on 2Ω seems odd. This

shows 0 - 1.7Ω or 1.7Ω - 5Ω etc, but is not what an electrician should be using, and it shows between two points, not a single reading, a bit pointless with a ring final, as pass is 1.37Ω so they can only test radials, with a MCB or 25 amp B type or less. One wonders why they are even made when only any good with 25 amp or less, as most UK use rings at 32 amp. Someone must waste £56 on them?

 

[JohnW2]

These are the reverse of each other, is it greater or less, If less, then no problem, if greater, then may be a problem.

I know that. However, he recently asked .....

Can you explain why a reading above 2 OHMS might cause a problem please?

...so I answered that question !

 

[Murdochcat]

Can you explain why a reading above 2 OHMS might cause a problem please? I'm sure you're correct in that he was referring to the rule rather than the actual reading he got. Many thanks for all the help here - it's much appreciated. I had an EICR done a few years ago when my CU was replaced - would their reading be on there somewhere?

I suspect you mean an EIC - do you have this to hand ?

 

[JohnW2]

I suspect you mean an EIC - do you have this to hand ?

Who (other than OP) knows whether your suspicions are correct - it's not uncommon for people to have, or be advised to have, an EICR undertaken prior to a CU change.

In any event, I don't think that an EIC issued at the time of a CU change would be all that much different from an EICR, would it? In particular (in context of this thread) it ought to have the same Schedule of test results in either case, oughtn't it?

 

[ericmark]

If I came to fit a shower, and the loop impedance is not within spec, I have two options, find out why and correct it, or say sorry can't fit the new shower.

Kohler Mira
recommend consulting a competent electrical engineer

Are they saying they are using incompetent engineers?
It's a bathroom, needs to be a scheme member to work in a bathroom in Wales, are they really using substandard labour in England?

 

[JohnW2]

If I came to fit a shower, and the loop impedance is not within spec, I have two options, find out why and correct it, or say sorry can't fit the new shower.

That's a reasonable statement but, of course, we don't know whether the EFLI was 'too high' - merely that it was "less than 2Ω".

It's a bathroom, needs to be a scheme member to work in a bathroom in Wales, are they really using substandard labour in England?

Even in England (as well as Wales) it would be notifiable work (since it would inevitably be within the bathroom zones) IF it qualified as an "addition or alteration to an existing circuit" in that location. However, I'm far from convinced that replacing an existing shower would so qualify - in either England or Wales, would it?

 

[Murdochcat]

Who (other than OP) knows whether your suspicions are correct - it's not uncommon for people to have, or be advised to have, an EICR undertaken prior to a CU change.

In any event, I don't think that an EIC issued at the time of a CU change would be all that much different from an EICR, would it? In particular (in context of this thread) it ought to have the same Schedule of test results in either case, oughtn't it?

I was really trying to determine if the op actually still has the document

 

[EFLImpudence]

Even in England (as well as Wales) it would be notifiable work (since it would inevitably be within the bathroom zones) IF it qualified as an "addition or alteration to an existing circuit" in that location. However, I'm far from convinced that replacing an existing shower would so qualify - in either England or Wales, would it?

Not in England as the classification for notification is "additions and alterations" (in a special location) but in Wales it is just "work"(which is not in a special location) which is not notifiable therefore it is notifiable.

EDIT - Not correct - see below.

 

[JohnW2]

I was really trying to determine if the op actually still has the document

I realise that, but the test result(s) which would interest us should be available from either an EIC or an EIC, shouldn't it?

 

[pete01]

As I explained, the EFLI with a B32 brewaker should be no greater than 1.09 Ohms.

If it is higher than that (and certainly if it is above 2 Ohms), then, in the event of some touchable metal becoming 'live' as a result of some fault (hence presenting a risk of electric shock), the breaker would not necessarily disconnect the supply (to make things safe) as rapidly as required by regulations (which is well under 1 second).

What about the rcd?

 

[JohnW2]

Not in England as the classification for notification is "additions and alterations" (in a special location) but in Wales it is just "work"(which is not in a special location) which is not notifiable therefore it is notifiable.

Good point - I'd forgotten that the original (still current in Wales) wording was just 'work', rather than the (current in England) 'additions and alterations').

There is, of course, no formal definition of 'work' in the Building Regs, but common sense would suggest that replacing an existing show would probably qualify. However, I seem to recall (maybe incorrectly?) discussion here about whether 'mere replacement of something faulty' (other than a CU) actually attracted a need for notification, even if it involved 'work' in a special location?

If there were a light with replaceable lamp/bulb within zones of a bathroom, would you say that (the 'work' of) replacing that lamp/bulb would be notifiable?

 

[denso13]

However, I'm far from convinced that replacing an existing shower would so qualify - in either England or Wales, would it?

https://www.gov.wales/sites/default/files/publications/2019-05/building-regulations-guidance-part-p-electrical-safety.pdf

 

[EFLImpudence]

Good point - I'd forgotten that the original (still current in Wales) wording was just 'work', rather than the (current in England) 'additions and alterations').

There is, of course, no formal definition of 'work' in the Building Regs, but common sense would suggest that replacing an existing show would probably qualify. However, I seem to recall (maybe incorrectly?) discussion here about whether 'mere replacement of something faulty' (other than a CU) actually attracted a need for notification, even if it involved 'work' in a special location?

If there were a light with replaceable lamp/bulb within zones of a bathroom, would you say that (the 'work' of) replacing that lamp/bulb would be notifiable?

No, just found Schedule 4 specifically states replacing electrical equipment is not notifiable.

 

[JohnW2]

What about the rcd?

I mentioned that, early on ....

That [the RCD] is what is making the circuit 'safe to use' (if the EFLI is too high for the 40A breaker to make it totally 'safe').

However, it is generally not acceptable (other than in a TT installation) to rely on an RCD as the primary means of fault protection. If it were acceptable then, in these days of ubiquitous (almost 'universal') RCD protection fo circuits, we could nearly always allow any/all final circuits to have a Zs which was 'up in the clouds'

 

[JohnW2]

View attachment 406775

View attachment 406776

View attachment 406777

https://www.gov.wales/sites/default/files/publications/2019-05/building-regulations-guidance-part-p-electrical-safety.pdf

Thanks. That confirms what, as I wrote, I suspected!

Kind Regards, John