High Ze - DNO added an RCD!

[Kevin]

We've had a couple of jobs like this lately, where we have reported a high Ze reading back to the DNO. They have subsequently come and fitted a 100mA RCD between the meter and the CU.

I would have thought they would need to find the reason for the high values instead. Surely an RCD is used a supplementary protection, not primary. The job I looked at was a TNC-S system, so logically thinking, wouldn't a high Ze value possibly indicate a problem with the neutral?

Also, obviously the problem of the high Ze remains, so Zs readings may well be over the accepted limits..then how am I supposed to complete a test certificate??

many thanks

K

 

[IQ Electrical]

Your Zs readings are covered by the addition of the RCD (max 500 Ohms).

I would expect the 100mA RCD to be a temporary measure in the interim while investigative work is carried out.

 

[Kevin]

Thanks for the reply.

So you would be happy to sign a test cerificate, or a periodic if the Zs readfings were too high, as long as there was RCD protection? Or would you contact the DNO, and establish if they were coming back to rectify the problem first ?

K

 

[Deleted member 26818]

I doubt the DNO will actually conduct any further investigation.
Your problem, will be in the future when the RCD plays up, who will be responsible for replacing the RCD?

 

[IQ Electrical]

On the basis of the RCD, your Zs readings will comply because your disconnection times are met by that device.

Your PIR will show how compliance was achieved.

The DNO normally use an RCD as a temporary measure when Ze is slightly above the agreed maximum.

What was Ze out of interest?

 

[IQ Electrical]

I doubt the DNO will actually conduct any further investigation.
Your problem, will be in the future when the RCD plays up, who will be responsible for replacing the RCD?

How is that his problem?

As long as the DNO supplied and installed device is noted on your 'comments' section then you 've done exactly what would be expected of you.

 

[Kevin]

The one job I went to it was 1.11

My thoughts though, are that there could well be an issue with the incoming neutral, as it's TNC-S.

Not sure how we would complete an installation certificate, if one was ever required, would a comment on the existing installation suffice ?

 

[IQ Electrical]

Yes 'following our report of an exceeded max Ze reading, the DNO supplied and installed a 100mA RCD. Our certification was carried out with this device in place'

 

[JD6400]

If i were you i would try to find out if your DNO are planning to come back in the near future to sort out the fault . If not i would look at it as a latent fault and swap it to a stake . It could easily be a poor neutral joint thats on the way out , depending on your bonds could be bad mojo in that house !

 

[Kevin]

Nice one, thanks.

Like Spin said, I have my doubts the DNO will be back, so I want to make sure we're covered.

K

 

[Deleted member 26818]

How is that his problem?

No of course, it will be the client's problem.

I've seen this in the past, and the hassle getting the DNO to accept that the RCD was their equipment was unbelievable.

 

[Kevin]

If i were you i would try to find out if your DNO are planning to come back in the near future to sort out the fault . If not i would look at it as a latent fault and swap it to a stake . It could easily be a poor neutral joint thats on the way out , depending on your bonds could be bad mojo in that house !

Could be, tenant was also complaining of power fluctuations, though no evidence of it whilst I was there of course. Have now passed it back to the DNO.

 

[AlanWirral]

Sounds funny to me? After initial testing (pre board change) unless the Zs's were well within the limits i'd be thinking about walking away until the problem was solved by the DNO.

Like said though if the results are fine and you have noted the problem then it's all good.

 

[Amp David]

I doubt the DNO will actually conduct any further investigation.
Your problem, will be in the future when the RCD plays up, who will be responsible for replacing the RCD?

Good point as the DNO won't want to know as its after the meter.

SOunds like a kop out to me!

 

[malcolmsanford]

It may not be a neutral problem at all, after all a PME system is just a glorified TT system. They may have problems with the stakes/spikes they had fitted, there may have been construction work further upstream that meant stakes were removed or having to be resited.

I go along with IQ here I think this is something temporary. I can not imagine the DNO just fitting an RCD and walking away. There may be a failing neutral but I bet you they are trying to find what it is and how to fix it.

 

[DurhamSparky]

High ZE = YOU Found a Problem
DNO Contacted and Responded = No Longer YOUR Problem
Complete Test Certs as Usual and Note the Certificate about the Problem with High ZE and DNO

Walk Away with head held High!

 

[IQ Electrical]

It may not be a neutral problem at all, after all a PME system is just a glorified TT system. They may have problems with the stakes/spikes they had fitted, there may have been construction work further upstream that meant stakes were removed or having to be resited.

I go along with IQ here I think this is something temporary. I can not imagine the DNO just fitting an RCD and walking away. There may be a failing neutral but I bet you they are trying to find what it is and how to fix it.

The problem here, as it always is when a DNO is involved, is communication or a lack of it!

The DNO should be writing to the client, acknowledging that there was a problem, detailing what they did to make it safe and if that repair was a temporary measure, how they are dealing with the fault.

These mythical people just turn up, alter the characteristics of YOUR installation, leave no written evidence or certification for what was done and that could be the last you hear of it!

There's even an argument that the addition of an RCD 'between the meter and consumer unit' is notifiable

 

[malcolmsanford]

The problem here, as it always is when a DNO is involved, is communication or a lack of it!

The DNO should be writing to the client, acknowledging that there was a problem, detailing what they did to make it safe and if that repair was a temporary measure, how they are dealing with the fault.

These mythical people just turn up, alter the characteristics of YOUR installation, leave no written evidence or certification for what was done and that could be the last you hear of it!

There's even an argument that the addition of an RCD 'between the meter and consumer unit' is notifiable

Totally agree the DNO do not make themselves any friends with some of the attitude that is taken. Though far from being a red radical I felt that once again selling off the electrical grid system as not in our best interests, instead of dealing with a Central Electricity Board you now have to deal with several different ones, and then on top the supply companies who look after meters.

I have to say that at first I thought this thread was going to be about TN-S systems, as is was quite often found that these older ones had ELCBs fitted as well and by the DNO, but if I remember rightly these were before the meter, I maybe wrong with that.

Lol just see the DNO getting to grips with Part P ..................

 

[topquark]

Agreed, it should never have been sold off. As soon as it was the overidding motive became profit ... not in the consumers best interest!

 

[trebor]

I cant actually believe this, the ESQCR requires the DNO to maintain the Ze below the maximum of 0.35 for 100a TN-C-S system if they are supply the earth facility
Is it an S type RCD? they have fitted?
If not why bother to fit the 17th edition split ccu`s as there is now no dicrimination with the supply
Are they going to pop around once a quarter and press the test button on their rcd

This can not be acceptable as a permanent solution, if it was my job I would kick up a fuss about it and if nothing was done have their rcd removed and fit an s type 100ma as my main switch

 

[IQ Electrical]

ESQCR doesn't actually specify any max Ze values, the values are broad targets from an 'engineering agreement'.

Amazingly, there is no 'regulation' to force a DNO to comply with the 'engineering agreement' values!

 

[Chr!s]

I cant actually believe this, the ESQCR requires the DNO to maintain the Ze below the maximum of 0.35 for 100a TN-C-S system if they are supply the earth facility

ESQCR mentions no max figures for tncs

This can not be acceptable as a permanent solution, if it was my job I would kick up a fuss about it and if nothing was done have their rcd removed and fit an s type 100ma as my main switch

Not too much you can do about, you could TT it.

Is it an S type RCD? they have fitted?
If not why bother to fit the 17th edition split ccu`s as there is now no dicrimination with the supply
Are they going to pop around once a quarter and press the test button on their rcd

The ESQCR requires equipment of the dno and suppliers to ensure their equipments meets BS 7671, so an s type would ensure this.
If you have a 100 fuse and your ZE is 0.55 ohms this may be down to network parameters, but this wouldn't comply with BS7671, so they stick an rcd in to comply

 

[Chr!s]

Beat me to it