Fault at premises

rooster79

I was intrigued reading your posts so I was wondering could you help me out with an issue I'm having at the mo

To start I got a call to take a look at a pub for a friend of mine because his neighbour roughly 300m away that owns a milking parlour was concerned about his cattle getting shocks and had his premises checked by a spark and seemed to be ok, when I tested the pub supply I got the following readings
• Independant earth and neutral at meter 1.3volts
• grip ammeter around neutralising earth in 16 T+E going from meter to consumer unit 4.5 amps
• grip ammeter around consumers earth rod 2 amps
• Loop impedance on ESB cutout .32 ohms

As you can see loop is within standard so my question is would these readings in pub be enough to cause shocks in milking parlour noting that it is fed from same transformer and how do I go about rectifying the problem...

Bruthal

rooster79 wrote: »

I was intrigued reading your posts so I was wondering could you help me out with an issue I'm having at the mo

To start I got a call to take a look at a pub for a friend of mine because his neighbour roughly 300m away that owns a milking parlour was concerned about his cattle getting shocks and had his premises checked by a spark and seemed to be ok, when I tested the pub supply I got the following readings
• Independant earth and neutral at meter 1.3volts
• grip ammeter around neutralising earth in 16 T+E going from meter to consumer unit 4.5 amps
• grip ammeter around consumers earth rod 2 amps
• Loop impedance on ESB cutout .32 ohms

As you can see loop is within standard so my question is would these readings in pub be enough to cause shocks in milking parlour noting that it is fed from same transformer and how do I go about rectifying the problem...

You should have tested both L and N from meter to consumer unit as well, which would indicate if any earth faults by the readings being different.

Current as high as you got on neutralising link would suggest some earth leakage within the pub installation, and/or small overhead lines supplying the pub.

rooster79

robbie7730 wrote: »

You should have tested both L and N from meter to consumer unit as well, which would indicate if any earth faults by the readings being different.

Current as high as you got on neutralising link would suggest some earth leakage within the pub installation, and/or small overhead lines supplying the pub.

What results should I expect to find and how do I carry out test on pubs tails

Bruthal

rooster79 wrote: »

What results should I expect to find and how do I carry out test on pubs tails

I meant test the current in both L and N, the same way you did on the earth and neutralising wires, with the grip ammeter.

If no earth leakage, both L and N currents should be the same.

But anyway, this shouldn`t cause shocks to be perceived at the other installation if it is properly installed/wired.

Is it overhead lines supplying the pub?

rooster79

rooster79 wrote: »

What results should I expect to find and how do I carry out test on pubs tails

Sorry Robbie to answer your question yes pub is supplied by oh line, readings on the pub tails were
• 16s tail from meter to CU live 60 amps
• 16s tail from meter to CU neutral 55 amps
• Neutralising link 5 amps

Bruthal

rooster79 wrote: »

Sorry Robbie to answer your question yes pub is supplied by oh line, readings on the pub tails were
• 16s tail from meter to CU live 60 amps
• 16s tail from meter to CU neutral 55 amps
• Neutralising link 5 amps

Yea so it looks like 5 amps earth leakage, and its all coming back through the earth`s from the circuits in the pub. Thats why you are seeing 5 amps higher in the live to DB (distribution board)

Switching off a circuit at a time until that 5 amp difference disappears, might tell you what circuit or circuits it is, if you want to look.

Some items tend to have some leakage, but 5 amps is a fair bit from a 65 amp loading. Is it single phase?

Could be a neutral to earth short in a circuit possibly.

That should`t affect other installations connected to the same transformer really though, in answer to your main question.

rooster79

robbie7730 wrote: »

Yea so it looks like 5 amps earth leakage, and its all coming back through the earth`s from the circuits in the pub. Thats why you are seeing 5 amps higher in the live to DB (distribution board)

Switching off a circuit at a time until that 5 amp difference disappears, might tell you what circuit or circuits it is, if you want to look.

Some items tend to have some leakage, but 5 amps is a fair bit from a 65 amp loading. Is it single phase?

Could be a neutral to earth short in a circuit possibly.

That should`t affect other installations connected to the same transformer really though, in answer to your main question.

I agree that it's most likely a neutral / earth fault , but I would have to disagree regarding it not affecting milking parlour. If I am seeing 4/5 amps in neutralising link and if earth resistance of milking parlour is less than earth at transformer you would have to assume some fault current is finding its way up the parlours earth thus importing the fault???

Bruthal

rooster79 wrote: »

I agree that it's most likely a neutral / earth fault , but I would have to disagree regarding it not affecting milking parlour. If I am seeing 4/5 amps in neutralising link and if earth resistance of milking parlour is less than earth at transformer you would have to assume some fault current is finding its way up the parlours earth thus importing the fault???

Think about it though. 60 amps into pub on live. 55 returns on neutrals in circuits. 5 returns via neutral earth short in pub, which is simply 5 amps diverting to the earth wire in a circuit because it is now in parallel with the neutral wire of that circuit due to being in contact with it.

The 5 amps is simply coming back via the CPC to the DB earth bar instead of on the circuit neutral wire, and back onto the main neutral via the neutralising connection. This itself on its own will not make one bit of difference to the other installation connected to the transformer.

The milking parlour possibly has its own earthing problems. It could have an earth fault from live to earth, or earth leakage from an item, and the metal in the parlour is not properly earthed.

AN electric fence badly installed is another thing that causes problems.

But either way, any shock problems at the milking parlour are likely to be problems within that installation.

Bruthal

rooster79 wrote: »

If I am seeing 4/5 amps in neutralising link and if earth resistance of milking parlour is less than earth at transformer you would have to assume some fault current is finding its way up the parlours earth thus importing the fault???

The 5 amps in the pub neutralising link is just 5 amps that is not coming back on the pub circuit neutrals. It is still ending up with 60 amps going back to the transformer via the main neutral, and so is absolutely no different than if 60amps went into pub on live, and 60 amps comes back on neutral to DB (with no neutral to earth fault), and 0 amps on neutralising link.

Current on the neutralising link of one installation does not suddenly start causing problems on other installations. Its just returning neutral current from the pub load and nothing more, even if some of it is taking the wrong path within the pub.

rooster79

robbie7730 wrote: »

Think about it though. 60 amps into pub on live. 55 returns on neutrals in circuits. 5 returns via neutral earth short in pub, which is simply 5 amps diverting to the earth wire in a circuit because it is now in parallel with the neutral wire of that circuit due to being in contact with it.

The 5 amps is simply coming back via the CPC to the DB earth bar instead of on the circuit neutral wire, and back onto the main neutral via the neutralising connection. This itself on its own will not make one bit of difference to the other installation connected to the transformer.

The milking parlour possibly has its own earthing problems. It could have an earth fault from live to earth, or earth leakage from an item, and the metal in the parlour is not properly earthed.

AN electric fence badly installed is another thing that causes problems.

But either way, any shock problems at the milking parlour are likely to be problems within that installation.

But I also have roughly 2 amps heading down the pubs earth rod which I think is finding its way back to the transformer via the milking parlour earth which might have a lower earth resistance than the transformer earth

2011

rooster79 wrote: »

But I also have roughly 2 amps heading down the pubs earth rod which I think is finding its way back to the transformer via the milking parlour earth which might have a lower earth resistance than the transformer earth

Electricity will take the paths of least resistance. From the pub and then back through the earth rod in the milking parlour is not one of these paths.

To prove this:
Turn off the power in the milking parlour and all currents in the milking parlour will disappear.

RoundyMooney

rooster79 wrote: »

But I also have roughly 2 amps heading down the pubs earth rod which I think is finding its way back to the transformer via the milking parlour earth which might have a lower earth resistance than the transformer earth

This.

The concept that faults in one installation do not manifest themselves in another (which I'm sure Robbie7730 isn't saying, btw), is ultimately a false one.

Particularly in milking parlours with a large mass of conductive metal, generally and hopefully, a better earthing system, and some rather large and electrically sensitive end users.

Trying isolation, circuit by circuit, in the pub in the first instance, is the way to go initially. But don't hang about. If the fault deteriorates (ironically, any attempt to improve the bonding or earth resistance within the farm may actually make things worse!) and this guy starts losing dairy cows, he may get understandably upset.

But rule nothing out. You have shown a logical and competent approach to this which many electricians fail to do, and that's half the battle. Let us know either way

Bruthal

rooster79 wrote: »

But I also have roughly 2 amps heading down the pubs earth rod which I think is finding its way back to the transformer via the milking parlour earth which might have a lower earth resistance than the transformer earth

Current that goes down the earth rod, will also simply end up back in the neutral conductor back to the transformer.

There is no way I can see 2 amps would divert down the earth rod and up to the milking parlour earth rod and back to the transformer that way, when there is a perfectly functioning solid neutral from the pub earth rod direct to the neutral supplying the pub, via the neutralising link.

What can cause this current down the earth rod is small overhead lines I mentioned earlier and asked you if they were supplying the pub. Small overhead lines can mean the neutral supplying the pub can be a couple of volts above earth potential, and so a small amount of the current coming back on the neutral from pub is diverting down the earth rod and through the ground, and back to the transformer via its earthing of the neutral and possible other earthing points. Its still surprising its 2 amps though, especially as you said 60 amps in, 55 back to db on neutral, and 5 on neutralizing link. You might have been rounding figures a little for posting probably.

But overall, id say the parlour itself has a problem if metal in it is causing shocks.

Bruthal

RoundyMooney wrote: »

This.

The concept that faults in one installation do not manifest themselves in another (which I'm sure Robbie7730 isn't saying, btw), is ultimately a false one.

No what I am saying is reading some amps on the neutralsing link of an installation where the current in and out is matching, wont be causing problems in another installation. That is simply neutral current diverting through an earth due to neutral to earth short in the installation (pub)

That wont have any effect outside the pub by itself.

Bruthal

If 2 amps flowing down the pub earth rod was somehow flowing up into the earthing of the milking parlour, then the milking parlour must be neutralized for this to happen.

As such, if 2 amps flowing into the neutralizing connection at the milking parlour is causing such problems, then what about the milking parlours own load current on the neutral which flows through its neutralizing point?

Its simply not feasible in my opinion for 2 amps down the pub earth rod to cause the milking parlour its problems without the parlour having some problems itself.

Bruthal

2011 wrote: »

Electricity will take the paths of least resistance. From the pub and then back through the earth rod in the milking parlour is not one of these paths.

It could be a possible route if the pole transformer itself has its earthing of its neutral failed and so the 2 amps down the pub earth rod can only be going up the parlour earth rod and to the transformer. And also depending on how close the pub is to the parlour compared to the position of the transformer relative to both.

But like you say, it would seem an unlikely route for 2 amps to take when the pub is only taking 60 in total, and has a good neutral straight back to the transformer.

To prove this:
Turn off the power in the milking parlour and all currents in the milking parlour will disappear.

A good suggestion.

And Id still say that if the parlour has an intact neutralizing connection, which it would have to have for the 2 amps from the pub earth rod to take that route, then 2 amps flowing this way would have no effect on the parlour, as its own neutral load would be far in excess of this 2 amps.

The parlour itself must have problems within the installation.

2011

rooster79 wrote: »

• 16s tail from meter to CU live 60 amps

= total current into the pub

• 16s tail from meter to CU neutral 55 amps
• Neutralising link 5 amps

Therefore 55 + 5 = total current returning from the pub.

So all of the current returning have now been accounted for within the pub. This is why I do not think that any of this is flowing up an earth rod 300m away in a milking parlour.

• grip ammeter around consumers earth rod 2 amps

This current in my opinion is making up part of the 5 amps in the neutralising link. The other 3 amps are returning through multiple paths to the earth bar and from there through the neutralising link.


Clearly both premises need to be checked out fully as a matter of urgency. It only takes about 25 volts can to kill a cow! As little as 1 volt can reduce milk production.

M cebee

5 amp diverted through neutralizing link is easily explained.
wiring fault,
crossed N-E in a 1kw lighting load
And doesn't seem to pose any hazard to a neighbouring installation

don't see how 2 amp would divert down the rod there though

M cebee

first thing i'd do anyhow after getting those readings
switch off pub,disconnect neutral
check reading on rod(earthing conductor)again

Bruthal

2011 wrote: »

So all of the current returning have now been accounted for within the pub. This is why I do not think that any of this is flowing up an earth rod 300m away in a milking parlour.

Even if it was, it cant have any effect, it would only be 2 amps flowing on the same path in the milking parlour, as all the neutral current from the parlour itself.

Bruthal

Put the same grip ammeter around a wire supplying a 100 watt bulb, and see what it reads as well.

Bruthal

M cebee wrote: »

don't see how 2 amp would divert down the rod there though

With small overhead lines and a longish run, the neutral might be a couple of volts above ground potential at the house, compared to at the transformer.

Some small current will take the rod path and would increase probably, as the volt drop on the supply lines increases. The actual amount would be the same ratio (in reverse) as the neutral conductor impedance//earth rod path impedance.

So for 60 (58) amps back on neutral from pub, 2 amp back on earth rod, thats 30/1.

So the earth rod path would need to be 1/30th the impedance of the neutral conductor path, to see 2 out of 60 amps divert that way, which would seem a bit extraordinary for it to have 2 amps down one earth rod to go up another as a way back to the transformer.

A measurement of currents ustream of neutralizing connection, of L and N, maybe at the meter, will also be a way of seeing is any current missing in the neutral at that point. Although can probably only be measured before neutralizing point if singles are supplying the meter cutout. But L compared to N+Neutralizing link will tell if any is missing, which will be going to the earth path.

A loop impedance test with earth rod connected, compared to disconnected, would be interesting. A test of the grip ammeter on a low current item such as the roughly 0.5 amp 100w bulb is worthwhile too.

M cebee

"So the earth rod path would need to be 1/30th the impedance of the neutral conductor path, to see 2 out of 60 amps divert that way, which would seem a bit extraordinary for it to have 2 amps down one earth rod to go up another as a way back to the transformer"

the other way round-30 times isn't it?
op said the loop-impedance at cut-out(how'd he measure that:)) is 0.35,which is a good reading

dunno are these low readings always reliable info
http://www.fluke.com/Fluke/usen/Clamp-Meters/Fluke-360.htm?PID=56072&trck=360
i'd have more faith in one of these

M cebee

he should switch off and disconnect the installations anyhow
see which one is actually causing the fault condition

Bruthal

M cebee wrote: »

the other way round-30 times isn't it?

Yes, earth rod path 30 times the impedence of the neutral path I meant. Reverse ratio of the currents.

op said the loop-impedance at cut-out(how'd he measure that:)) is 0.35,which is a good reading

Yes part of the loop is the neutral path and earth rod path combined. It would be interesting to see if the earth rod disconnected would change it much. Normally with mini pillars and decent size underground cables and multiple neutralizing points along neutrals, it probably wont, but with long runs of small overhead lines and one or 2 premises from a pole transformer, maybe it would.

Either way, 2 extra amps on the neutral side of the parlour would mean little in terms of causing voltage on metalwork, as it is on the same conductor any hypothetical earth rod current from the pub would take, as the parlours own neutral current.

Imo any current down the earth rod is simply going back to the transformer this way. In theory, it will take every path possible, but any possible current finding its way back through the parlour, wont have any effect on the parlour metalwork, that the parlours own neutral current wont itself cause.