RCD problem discovered and cooker installation query

[bhwh]

We have had a company fit a new gas/electric cooker, including control panel. They are now requesting payment but I have two issues:

1. The wire that they have installed from the CU to a cooker switch then on to a cooker outlet, has been chased into the wall where I intend to install splashback. However behind the units etc they have not used conduit so that the cable is visible and just clipped to the wall. Whilst this is not visible and therefore not an 'eye sore', is it allowed? I had envisaged it being encased in plastic conduit until it sinks into chasing.

2. On installtion, they discovered a fault with the CU which had not been a problem before:

we have found faults on the RCD switch, this is breaking down and tripping out to soon, eventually this will fail completely, also the main earth reading is on the high side of normal, this indicates that the earth rod isn’t fitted correctly and could cause problems with nuisance tripping.

If we can get a replacement trip we can then replace this otherwise it will mean a new distribution board and complete test- we will get back to you on the availability.

Does this sound reasonable to you? I appreciate that without seeing/testing it yourself, it may be difficult to answer this one...

Many thanks

 

[flameport]

Cables clipped to the surface are acceptable, provided they are not likely to be damaged - so behind the units is fine.

RCD - these can go faulty, although you need to find out what the test results actually are, rather than them saying 'tripping out too soon'.

Same with the earth rod - what was the reading they obtained, and what were they measuring?
An earth rod can't really be fitted incorrectly. They do corrode eventually and it may need replacement.
However there is no way an earth rod could cause nuisance tripping.

Can you post a picture of the existing RCD/ distribution board etc.?

 

[sparkyspike]

1. It is quite normal to have cables running surface under the counter. At least you know where they are. Many electricians would put it in trunking if it is visible when you open a door.

2. It all depends on the fault. If it is a faulty RCD, then it needs to be replaced. RCDs should be available for pretty much all relatively modern boards.

It may be a wiring fault or even the new appliance. Have they confirmed this with proper testing?

High earth loop at the supply is a serious problem - but they don't say it is too high, just higher than normal. Did they give a figure? TT systems can have a fairly high loop impedance and still be ok if there is full RCD protection.

 

[sparkyspike]

By the way - they should really have measured the external loop impedance before starting. Although it's not their fault that there is a possible problem with the RCD and the earth rod, it is still their responsibilty to see that the problems are corrected.

What is the value of external loop impedance (did they give it to you?)?

 

[bhwh]

Thanks for both your replies.

1. Conduit - if it's all ok to have surface mounted cable just clipped to the wall behind kitchen cupboards, then it's fine with me! At least there'll be no drills going though'em!

2. RCD - the CU is Crabtree and installed (I guess) within the last 10-20 years. I'm due to be giving the company a call tomorrow to see if he could get a replacement RCD. He seemed pretty doubtful over the phone and said that these manufacturers like you to replaced the whole thing (more £££). Wait and see...

As for the earth rod business...I'm afraid that's completely over my head. Just wanted to see what you guys thought... I haven't asked for the test results and actually I don't know what 'external loop impedance' is!!! So I'm not sure how useful that would all be to me (except I could post it here I suppose!)

Do you suggest I ask for these details in any case?

 

[flameport]

Crabtree 10-20 years old means it is very likely that a replacement can be obtained. Even if not, this doesn't have to mean the entire board requires replacement.

You should receive an electrical installation certificate with the test results for the new circuit, the RCD and the earth rod on it. This is required regardless of whether they replace the RCD or not.

 

[Steve]

2. RCD - the CU is Crabtree and installed (I guess) within the last 10-20 years. I'm due to be giving the company a call tomorrow to see if he could get a replacement RCD. He seemed pretty doubtful over the phone and said that these manufacturers like you to replaced the whole thing (more £££). Wait and see...

No they dont, thats why they are modular. If they wanted you to replace the whole lot, they'd form it from one huge piece of plastic.

As for the earth rod business...I'm afraid that's completely over my head. Just wanted to see what you guys thought... I haven't asked for the test results and actually I don't know what 'external loop impedance' is!!! So I'm not sure how useful that would all be to me (except I could post it here I suppose!)

Do you actually have an earth rod?

loop impedance is the resistance of the flow of electricity through the earth rod, to earth. When you have an electrical fault to earth, you need the resistance to be low enough to trip the breaker. If the resistance is too high, the breaker wont trip and the fault will continue.


Sorry to be negative, but under no circumstances let them replace the whole consumer unit. They are having you good and proper if you do. Let them charge for the work done, and the RCD if they "can source" one. If they cant, tell them you will get anotehr spark to look at it.

 

[bhwh]

Thanks for the explanation Steve.

You're last comment basically sums up what I felt without really fully understanding the situation. I'll see if he can replace the RCD and if not pay up for the work done, get a certificate for what they did and say thank you very much!

Cheers

 

[ban-all-sheds]

However there is no way an earth rod could cause nuisance tripping.

A poorly working one could prevent it....