Earth Loop Impedance Test and problem with power supply

[Maverick777]

Hi,

Our main fuse from the power distributor blew and Western Power attended and replaced. During this visit they established that their was a problem with reverse polarity and that when the RCD was installed the tails in the grey twin cable were connected red-black in the top of the consumer unit.This particular type of unit needs to be black-red. It is probable that we removed the external fuse to enable the RCD to be installed and on completion the fuse was replaced. However polarity checks showed reverse polarity.To correct this the tails were reversed on top of the external cut-out and this cured the problem. At this stage there was no electrical danger and it stayed that way until the shower developed a fault last week and the crossed tails were spotted.

I've had an electrician attend who spent all day testing and the Earth Loop Impedance Test showed a reading of 363 Ohms which I believe is very high. He has recommended changing the circuit board at a cost £350.00. However this does not gurantee that the problem will be resolved. Please advise.

Thanks

 

[Plonker 3]

Has he given you any sort of paperwork?

I take it you mean he took the Ze or external loop impedance at your distribution board.

It sounds like it could be a TT system where the DNO doesn't supply an earth but it is provided locally via a earth rod. If that is the case then putting new earth rods in until the readings are satisfactory is the best solution.

If it is either a TN-C-S or a TN-C then it is the distributors responsibility to proved the earth in which case contact them.

As for the reverse polarity has that been resolved with a certificate issued?

 

[Paul.M]

Apart from the reverse polarity has the electrician said why you need a board change?

 

[Geordie Spark]

Apart from the reverse polarity has the electrician said why you need a board change?

KERCHING !!!!!!!!!!! perhaps?

 

[Paul.M]

KERCHING !!!!!!!!!!! perhaps?

I didn't want to insinuate that it came down to money without knowing all the facts but KERCHING is the odds on favourite.

 

[Engineer54]

One things for absolute sure, ...A board chance isn't going to solve the high Zs value!!
As already been suggested, this is in all likelihood a TT system that has been badly installed in the first place. Having said that, is there any bonding to the main water/gas services in place??

I'm going to make an assumptions now!! ....I wouldn't expect such a high Zs with both of these services being bonded back to the MET, which means you ''Don't have'' any bonding in place!!

Your living very dangerously on the edge there i'm afraid, and totally relying on a single RCD device. I'd get your electrician back, and start asking him some very relevant questions, ....Like did you not notice i have no bonding conductors to my main water and gas services. And what is the Ze of my installation...lol!!! Those high Zs values should have rang alarm bells, and should have led him, to be checking main earthing and bonding conductors, before talking about CU changes!!

If my assumption is correct, then i would seriously be thinking about a change of electrician, one that has a good reputation in your area.... lol!!

 

[Plonker 3]

I've had an electrician attend who spent all day testing and the Earth Loop Impedance Test showed a reading of 363 Ohms which I believe is very high. He has recommended changing the circuit board at a cost £350.00. However this does not gurantee that the problem will be resolved. Please advise.

Thanks

How does a new DB bring down the earth loop results?

 

[ACDC]

How does a new DB bring down the earth loop results?

It wont. (I assume your DB has RCD(s) installed by your op)

 

[Engineer54]

I've had an electrician attend who spent all day testing and the Earth Loop Impedance Test showed a reading of 363 Ohms which I believe is very high. He has recommended changing the circuit board at a cost £350.00. However this does not gurantee that the problem will be resolved. Please advise.
Thanks

Any chance of you posting a photo or two of your CU (front cover removed), and the supply cut-out?? This will give us all a much better understanding of what you have or don't have, and enable us to give, as is the best advise on how to proceed!!

My earlier post maybe totally wrong, but i don't think so, not going by that enormous 363 ohm value you have quoted!! lol!!

 

[Maverick777]

Hi,

Thanks one and all for your replies. I'm no expert, not even a good DIY'er. However having listened to the power distributors that attended (Western Power = WP) following the original power failure it would seem that whoever put the power into the house from the grid, put the wires in, the wrong way round which I believe caused the reverse polarity. WP advised that we get an electrician into check the system out as the fuse (circuit breaker) kept blowing on the shower, even now we can only use the shower for less than 3 minutes before it trips out. The electrician fitted a RCD device which means I can just switch it back on before it trips again. The electrician spent most of the day baffling me with science and carring out tests with is big yellow box thingy which gave a reading of 363.

He gave the reason for changing the consumer unit as the old one was dated as it relied on changing fuse wires and was prone to catching fire...ekk! He felt that the old consumer board and become a tangled mess and that somewhere along the line someone as wired into the system to provide power to the garage and used connectors used by Western Power and not installed a separate earthing rod into the garage.

No mention has been made of any bonding conductors to the main gas and water services. Sadly I do not know what all your abbreviations stand for:-

1. TT
2. MET
3. Ze
4. Zs

Also I have been given no paperwork.

Thanks in advance for your help...

 

[Plonker 3]

Sounds like he was trying to scare you into getting your distribution board changed.

When ever I talk to customers I try and keep it as simple as possible without using too much technical information. If the customer starts looking confused then I will give them a print out of some information that I may have on my computer to explain what I was trying to say.

Did he mention anything about earth rods or suppiers earth?

May be worth getting another spark in, post you location and there will be someone on here who could come round and look at it for you?

 

[Engineer54]

Here you go ....

1. TT =Earthing system by means of earth rod(s)
2. MET =Main earthing terminal
3. Ze =Earth loop impedance external (with all earthing conductors at MET disconnected)
4. Zs =Earth loop impedance internal (with all earthing conductors connected)

 

[Engineer54]

Photo's would clear-up a lot of the unknowns for us to advise you futher, on how to proceed on getting your installation back to a safe and operational level etc!!...

 

[Paul.M]

I'd be careful E54 about asking a self confessed "not good at DIY" (as the op as stated) to take off the cu panel to take a pic. I'm not having a go E54, I'm just saying that we need to draw a line somewhere and I believe we are now crossing it.

 

[Des 56]

Have a nose around the areas where both the gas and water services enter the dwelling and look for a fairly large green/yellow cable attached to a clamp on that service,note whether the services supplied enter the dwelling by means of plastic or metal pipes as well

See if a green/yellow cable exits the dwelling and is connected to what is showing of an earth spike in the ground

Look at the incoming supply and see if there is a sticker with PME written on it, also observe if there is a green/yellow entering the enclosure where the supply fuse is located

You may or may not be well advised about a change of consumer unit,these may give better protection for the occupier than the older fuse boards (which are still available for electrical installations) but a new consumer unit does not fix problems,it can in some circumstances highlight a fault that may not blow a fuse,but such things as your value of Ze at the supply is irrelevent to the decision to renew your new consumer unit or not

You would be well advised to enquire into the value of whatever person you have doing the tests to ensure they can back their attendance with related skills ,qualifications etc
This is true of all works carried out,but probably more so with the electrical industry as it stands, with so many pretend sparks roaming free,thats not to imply lack of competence in your present spark,but a generalisation only

 

[Engineer54]

I'd be careful E54 about asking a self confessed "not good at DIY" (as the op as stated) to take off the cu panel to take a pic. I'm not having a go E54, I'm just saying that we need to draw a line somewhere and I believe we are now crossing it.

Fair point, OK at least a photo of the CU then, and the power company Cut-Out/ meter installation... lol!!

 

[Maverick777]

From left to right: Consumer Unit; Breaker; Cowboy Unit to Garage; Garage

 

[SPARTYKUS]

How does a new DB bring down the earth loop results?

There are some new metal ones, that, well, have a spike on the bottom. They are waterproof so you can fit into the garden directly.

Also they use a new wireless technology, so no need to extend any cables (including tails, amazing I know!)

 

[Engineer54]

Doesn't look as if you have any earthing shown in these photo's, certainly none provided by the power company, so if there is an earth anywhere, it will be by earth rods (TT system).

Can you see ANY green and yellow cables any where around your fuse board area?? Or come to that where your main water service and gas service enters your house??

EDIT.... Just noticed...You have 2 power company supplies to your property?? How come, 2 meters as well??

 

[Maverick777]

Not sure I can see the earth, but it is PME certified with a sticker.

 

[Maverick777]

I can see the yellow and green cable from the power supply that enters the house. But none near the consumer unit in the house or the garage or gas supply, which is a worry as the cable from the consumer unit runs through the gas meter box to the garage.

 

[telectrix]

well, if the supply is PME, then your Ze should be lower than 0.35, nothing like the 300 odd you mentioned. something fishy here .

 

[Maverick777]

What do you mean that we have 2 power company supplies?

 

[Des 56]

Not sure I can see the earth, but it is PME certified with a sticker.

My eyesights not up to much these days but that sure as damn it looks like a green/yellow in that pic

It is very possible that if there are services requiring bonding they will be present,the terminal should only be used when the requirements are met


edit Just seen the other picture with the second supply?
It gets interesting

 

[Engineer54]

I can see the yellow and green cable from the power supply that enters the house. But none near the consumer unit in the house or the garage or gas supply, which is a worry as the cable from the consumer unit runs through the gas meter box to the garage.

Are you out in the country as opposed to being in a village or town?? I would almost certainly be getting back in touch with your power company and asking if PME earth connection is available at your location. If not, then you will need to install your own TT system by means of driving a rod or rods into the ground in your back garden preferably. You will NEED to bond your incoming water/gas services too as close to there entry point as possible (within 600mm) It certainly looks to me as if you have no means of earthing or bonding to your property. Your electrician should have been far more conserned about this than renewing your CU, that could have been done at a later date!!!

 

[Engineer54]

Not sure I can see the earth, but it is PME certified with a sticker.

My eyesights not up to much these days but that sure as damn it looks like a green/yellow in that pic

It is very possible that if there are services requiring bonding they will be present,the terminal should only be used when the requirements are met


edit Just seen the other picture with the second supply?
It gets interesting

Can't see anything coming out of either of the 2 cut-outs myself either...lol!!

 

[Engineer54]

oops just seen post 20!!


Seems you have 3 power company cut-out positions, not going to even ask how. But the cut-out where the meter is definitly has a PME connection to it. Now where that earth conductor goes, i haven't a clue, can't see any sign of an earth or bonding conductor in any of the other photo's

 

[Des 56]

I wrote the reply below but didn't post in case I made an idiot of myself,but I am less convinced (being the idiot that is)

This must be a real off day for me

I just looked through the 2 posts showing the pics and can now count 3 cut outs,I gather there must be 2 supplies and 2 cut outs and one home made jobbie

Perhaps

 

[Engineer54]

What do you mean that we have 2 power company supplies?

You seem to have a power company fuse cut-out in an external box, in your house by the fuse board and another in the garage by another CU.... 3 power company cut outs, ...So how come?? Most premises will have only one!!! lol!!

 

[Maverick777]

I believe the cut out is correct by the external box, the one by the fuse board and in the garage where installed by Bob the Builder many moons ago. I've looked at the one in the garage and it was bridged by some 15 amp fuse wire. So I assume it was not a bona fide electrician. Could this be the cause of the problem?

 

[Maverick777]

I think the two extra cut outs are the supply to the garage and not correct for the job.

 

[Engineer54]

Has your electrician looked at these cut-outs, ...come to that, what did the DNO have to say about them. That one by the main fuse board is certainly DNO concentric cable. Not many general domestic electricians would be touching such cable...

As for being the cause of your problem, i doubt it, but who knows where and how these supply cables have been connected to the incoming supply!! lol!!

EDIT... Can you isolate the garage CU from the main fuse board??

 

[Paul.M]

I've got a few things to say about this thread:-

First I would like to thank Maverick777 for actually posting up photos to give us all an in-depth picture of what your talking about. I/we wish that more people like yourself asking for help/advice put in as much effort as you. Well done.

A little praise to E54 that he didn't have a pop at me for suggesting that "we" (not him btw, all in this together) were crossing a line. Me and E54 have crossed swords in the past (and not like that) and its great to see us lot coming together to help out a home owner good enough to give us the info that we need.

Again to Maverick777, thanks for a new saying that I will use "cowboy cu to garage" love it and I will be using it in the future.

Btw get a proper sparky in to look at this mess. A cu change won't help your problems looking at the photos.

 

[Maverick777]

Hi,

It would be great if any of you were in the Blackwood area of Gwent. Why are some of you thinking that our house is supplied by two power companies as one meter in post 20 is of the gas and one the electric. Is this what you meant?

Thanks

 

[Maverick777]

This is what Western Power engineer said after a visit:-

Hi both,
When I visited again on Saturday morning the cause of the crossed polarity was obvious.When the RCD was installed the tails in the grey twin cable were connected red-black in the top of the consumer unit.This particular type of unit needs to be black-red.It is probable that we removed the external fuse to enable the RCD to be installed and on completion the fuse was replaced.However polarity checks showed reverse polarity.To correct this the tails were reversed on top of the external cutout and this cured the problem.At this stage there was no electrical danger and it stayed that way until the shower developed a fault last week and the crossed tails were spotted by Lloyd.
We have now reconnected the tails the correct way round.We also carried out trip testing on the RCD and found it faulty at required sensitivity,also it trips when the consumer unit DP switch is operated.This unit needs to be replaced.
The consumer unit is also old school and could be upgraded with a combined segregated unit but Beesleys will advise what options you have.
We will pay for the visits on Thursday and Saturday ,the remaining work is your responsibilty to settle directly with your Contractor.
regards

 

[GLENNSPARK]

Apart from the reverse polarity has the electrician said why you need a board change?

another example maybe of "electrician" condemning a C/U without any valid reason maybe?...lol.....reminds me of this PIR we got for this rented a bit back from this "sparky"..lol.......sparky that gave gas and water bonding using a single continuous 10mm conductor as a (1)....lolffs....

 

[GLENNSPARK]

This is what Western Power engineer said after a visit:-

Hi both,
When I visited again on Saturday morning the cause of the crossed polarity was obvious.When the RCD was installed the tails in the grey twin cable were connected red-black in the top of the consumer unit.This particular type of unit needs to be black-red.It is probable that we removed the external fuse to enable the RCD to be installed and on completion the fuse was replaced.However polarity checks showed reverse polarity.To correct this the tails were reversed on top of the external cutout and this cured the problem.At this stage there was no electrical danger and it stayed that way until the shower developed a fault last week and the crossed tails were spotted by Lloyd.
We have now reconnected the tails the correct way round.We also carried out trip testing on the RCD and found it faulty at required sensitivity,also it trips when the consumer unit DP switch is operated.This unit needs to be replaced.
The consumer unit is also old school and could be upgraded with a combined segregated unit but Beesleys will advise what options you have.
We will pay for the visits on Thursday and Saturday ,the remaining work is your responsibilty to settle directly with your Contractor.
regards

surely the option here would be to replace the RCD....if the C/Us good for continued service...then just being "old school" is not acceptable reason to replace it is it?....as long as its in good order (IP)...and disconnection times are being met......

 

[Engineer54]

Hi,

It would be great if any of you were in the Blackwood area of Gwent. Why are some of you thinking that our house is supplied by two power companies as one meter in post 20 is of the gas and one the electric. Is this what you meant?

Thanks

No, you just have a very weird set-up there with the amount of cut-outs you have in your installation. I'm guessing that the cable shown supplying the main fuse board was once where the meter was, and has now been moved to an external position, but have used the old existing cable to continue supplying the fuse board. Haven't a clue how the one in the garage got there, but suspect that is now being used as a sub-main from the main fuse box. As i say, very wired that the cut-outs have been left in place by the power supply company, they normally remove them when any changes have been made to there installation...

Sorry, but i'm rather a long way from your neck of the woods... lol!!

 

[Paul.M]

another example maybe of "electrician" condemning a C/U without any valid reason maybe?...lol.....reminds me of this PIR we got for this rented a bit back from this "sparky"..lol.......sparky that gave gas and water bonding using a single continuous 10mm conductor as a (1)....lolffs....

You posted at the same time as the op, post 35.

He's got it in writing from the electricity board! You need a new cu lol.

Again thanks for the pics but honestly get a proper electrician to investigate your electrics. I'm not in your area but I wish I was. Looks like an interesting case.

 

[GLENNSPARK]

that mem C/U may be hard to get an RCD for as they use an RCD incomer in those.....

 

[BillyTheSparks]

As most of the main subject has been covered, I thought I'd throw this in to the mix.

I'd also be concerned about that cable running through the gas meter box, it hasn't been sealed and it looks like it is a cavity wall box. So if there was a leak, it could leak into the cavity and cause an explosive enviroment.

I would call the gas company or a good plumber to see what can be done.


I don't want to scare any one by the way, it's just an observation

 

[Maverick777]

Below was received from Western Power

Hi Gary,

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​

​

Your home is supplied by the substation to the left of you rear garden a distance of approx 70m.Your service is PME and as such the earth and phase loops are the same conductors and should have a loop impedance of 0.35 ohms or less.With a value of 363 ohms I doubt anything would work.This value is at the meter position,not at an internal socket though.I'll get this external value checked anyway by the local team and will need the main fuse to be removed for a few minutes.If you decide when its convenient during normal hours there is no charge for this.​

​

​

I await your reply,thanks​

​

​

 

[Geordie Spark]

As most of the main subject has been covered, I thought I'd throw this in to the mix.

I'd also be concerned about that cable running through the gas meter box, it hasn't been sealed and it looks like it is a cavity wall box. So if there was a leak, it could leak into the cavity and cause an explosive enviroment.

I would call the gas company or a good plumber to see what can be done.


I don't want to scare any one by the way, it's just an observation

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