The reality is that you can't apply any of these designations to either the supply or the installation within the house in isolation, since the codes incorporate elements from both. They apply to the system as a whole. I never really liked the terms, as they don't, in themselves, always convey the exact picture (e.g. PNB) and they seem to have led to a lot of confusion. (They are not used over here, by the way.)
TN-C-S Distrubution Fault Symptoms?
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OOI, what do you use?
Nothing that's directly equivalent - Just like Britain before circa 1981. But all standard supply arrangements (120/240V single-phase 3-wire, 120/208V & 277/480V wye, 120/240V 4-wire delta etc.) are wired as the equivalent of TN-C-S anyway; there isn't the wide variation of earthing arrangements found in the U.K., and the TT arrangement is specifically prohibited by the NEC. Variations are only for particular special purposes, e.g. dedicated separately derived isolated-from-ground supplies in hospital operating theatres.
Which Clause is that? I can't find that prohibition.
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Not sure if it might have been moved in the last couple of editions, but in 2008 it can be found in 250.4(A)(5).
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Hello to everyone,
It took some time before i could get back to the mission.
Since the last time i posted, ive left the downstairs ring switched off and locked off, with normal safe isolation practices in place.
Purchased a Fluke 125 Clamp Meter, and have been using it to track current flow through the main earth bonding to the MCU. Their is current flowing along the main earth bond of of at least 500mA when i have checked, and it fluctuates, increasing as the evening moves in to peak usage for the grid. The main earth bond increased 0.53A to 1.44A when i had the main power off, with the live at 0.02A and the neutral at 0.02A. The micro tesla readings for the cables as bunch leaving the electricity cupboard was 4.8uT, seems high for a house with no power.
I also performed a test as i noticed strange readings a previous evening of 2.9A running through the main Earth bond, with the same cleaner running and lights and maybe a computer. This time i powered down the house, using only the cooker socket, switched on a 1200w Dyson cleaner.
The E = 1.77A, L=5.56A, and the N=5.47A, using the clamp meter.
I also had the Dyson running through a wattage meter, and recorded these results close to the same time
Voltage 237V AC, 5.05A, 50Hz.
I checked the downstairs ring main, and did a number of tests.
I disconnected the ends of r1, rn and r2 from the MCU, and measured from ends of each loop.
r1 loop = 0.53 R
rn loop = 0.43 R
r2 loop = 0.73 R Thinner earth wire (0.43 R x 1.67) = 0.72 R
I then disconnected the furthest socket in the ring, and confirmed loop a and loop b, and tested with a long lead end to end. Values don't include resistance of the leads.
r1-a = 0.34 R end to end rn-a = 0.27 R end to end r2-a = 0.46 R
r1-b = 0.18 R end to end rn-b = 0.16 R end to end r2-b = 0.28 R
The loop b has less sockets than loop a, in fact it would seem most of the load of the downstairs ring main, with the added spurs.
Next i reconnected the end socket, and performed a resistance check between line and neutral, with a connection block connecting the r1-a to rn-b, and r1-b to rn-a.
The calculated expected resistance for line to neutral was (r1 + rn)/4 = (0.53 R + 0.43 R)/4 = 0.24 R.
The calculated expected resistance for line to earth was (r1 + r2)/4 = (0.53 R + 0.73 R)/4 = 0.32 R
Socket 1 r1 + rn = 0.28 R r1 + r2 = 0.33 R
Socket 2 r1 + rn = 0.22 R r1 + r2 = 0.30 R
Socket 3 r1 + rn = 0.24 R r1 + r2 = 0.33 R
Socket 4 r1 + rn = 0.23 R r1 + r2 = 0.30 R
Socket 5 r1 + rn = 0.24 R r1 + r2 = 0.32 R
Socket 6 r1 + rn = 0.24 R r1 + r2 = 0.30 R
Socket 7 r1 + rn = 0.22 R r1 + r2 = 0.37 R
Ive only opened socket 5 so far, thats where i split the ring. I originally thought it was the mid point, but when i traced the sockets order, i quickly realised they wired all the kitchen sockets in series on the same side of the ring. I will proceed to open and check all the wiring of the sockets, and replace some of them likely.
I then rewired the ring to the MCU, and tested the insulation at 500v, which was a fail.
L1 to L2 = 0.06M R
L1 to L3 = 0.05M R
L2 to L3 = 0.04M R
I suspect there is an RCD socket in the shed, so im going to remove tomorrow and perform another insulation test, but the insulation test should have been at least >1M ohms. Ive also discovered the plumber installed the central heating pipes over the mains cables in the celling, some of the cables are resting on a radiator pipe, and have been for nearly 12 years.
Updated 18/11/2015 11:06
====================
I disconnected the shed RCD Socket, and the insulation results were:
L1 to L2 = 1.22 M ohms ( the value went up to between 8M and 10M, then dropped back to 1.22 M, so something might not be right i suspect)
L1 to L3 = 192 M ohms (Values kept climbing while holding test button, maybe because other devices connected on other breakers, dimmer switches and computers)
L2 to L3 = 200 M ohms (Values kept climbing while holding test button, maybe because other devices connected on other breakers, dimmer switches and computers)
I started investigating socket 1 in the kitchen, and discovered the wires are so tight, i can not even remove the socket from the pipe boxing. Then i looked above the cupboard above socket1, and discovered the kitchen fitter had not run a spur from socket1, but cut straight in to the ring and added another socket. The main wire colours are visible coming out of the back box, so he must have struggled. It might also be why the wires are so tight on the socket below.
The kitchen was fitted by a respectable kitchen fitters company 15 years ago.
=================================================
Forgive me if my electrical terminology is a bit off.
What do you guys think?
Yours gratefully.
It took some time before i could get back to the mission.
Since the last time i posted, ive left the downstairs ring switched off and locked off, with normal safe isolation practices in place.
Purchased a Fluke 125 Clamp Meter, and have been using it to track current flow through the main earth bonding to the MCU. Their is current flowing along the main earth bond of of at least 500mA when i have checked, and it fluctuates, increasing as the evening moves in to peak usage for the grid. The main earth bond increased 0.53A to 1.44A when i had the main power off, with the live at 0.02A and the neutral at 0.02A. The micro tesla readings for the cables as bunch leaving the electricity cupboard was 4.8uT, seems high for a house with no power.
I also performed a test as i noticed strange readings a previous evening of 2.9A running through the main Earth bond, with the same cleaner running and lights and maybe a computer. This time i powered down the house, using only the cooker socket, switched on a 1200w Dyson cleaner.
The E = 1.77A, L=5.56A, and the N=5.47A, using the clamp meter.
I also had the Dyson running through a wattage meter, and recorded these results close to the same time
Voltage 237V AC, 5.05A, 50Hz.
I checked the downstairs ring main, and did a number of tests.
I disconnected the ends of r1, rn and r2 from the MCU, and measured from ends of each loop.
r1 loop = 0.53 R
rn loop = 0.43 R
r2 loop = 0.73 R Thinner earth wire (0.43 R x 1.67) = 0.72 R
I then disconnected the furthest socket in the ring, and confirmed loop a and loop b, and tested with a long lead end to end. Values don't include resistance of the leads.
r1-a = 0.34 R end to end rn-a = 0.27 R end to end r2-a = 0.46 R
r1-b = 0.18 R end to end rn-b = 0.16 R end to end r2-b = 0.28 R
The loop b has less sockets than loop a, in fact it would seem most of the load of the downstairs ring main, with the added spurs.
Next i reconnected the end socket, and performed a resistance check between line and neutral, with a connection block connecting the r1-a to rn-b, and r1-b to rn-a.
The calculated expected resistance for line to neutral was (r1 + rn)/4 = (0.53 R + 0.43 R)/4 = 0.24 R.
The calculated expected resistance for line to earth was (r1 + r2)/4 = (0.53 R + 0.73 R)/4 = 0.32 R
Socket 1 r1 + rn = 0.28 R r1 + r2 = 0.33 R
Socket 2 r1 + rn = 0.22 R r1 + r2 = 0.30 R
Socket 3 r1 + rn = 0.24 R r1 + r2 = 0.33 R
Socket 4 r1 + rn = 0.23 R r1 + r2 = 0.30 R
Socket 5 r1 + rn = 0.24 R r1 + r2 = 0.32 R
Socket 6 r1 + rn = 0.24 R r1 + r2 = 0.30 R
Socket 7 r1 + rn = 0.22 R r1 + r2 = 0.37 R
Ive only opened socket 5 so far, thats where i split the ring. I originally thought it was the mid point, but when i traced the sockets order, i quickly realised they wired all the kitchen sockets in series on the same side of the ring. I will proceed to open and check all the wiring of the sockets, and replace some of them likely.
I then rewired the ring to the MCU, and tested the insulation at 500v, which was a fail.
L1 to L2 = 0.06M R
L1 to L3 = 0.05M R
L2 to L3 = 0.04M R
I suspect there is an RCD socket in the shed, so im going to remove tomorrow and perform another insulation test, but the insulation test should have been at least >1M ohms. Ive also discovered the plumber installed the central heating pipes over the mains cables in the celling, some of the cables are resting on a radiator pipe, and have been for nearly 12 years.
Updated 18/11/2015 11:06
====================
I disconnected the shed RCD Socket, and the insulation results were:
L1 to L2 = 1.22 M ohms ( the value went up to between 8M and 10M, then dropped back to 1.22 M, so something might not be right i suspect)
L1 to L3 = 192 M ohms (Values kept climbing while holding test button, maybe because other devices connected on other breakers, dimmer switches and computers)
L2 to L3 = 200 M ohms (Values kept climbing while holding test button, maybe because other devices connected on other breakers, dimmer switches and computers)
I started investigating socket 1 in the kitchen, and discovered the wires are so tight, i can not even remove the socket from the pipe boxing. Then i looked above the cupboard above socket1, and discovered the kitchen fitter had not run a spur from socket1, but cut straight in to the ring and added another socket. The main wire colours are visible coming out of the back box, so he must have struggled. It might also be why the wires are so tight on the socket below.
The kitchen was fitted by a respectable kitchen fitters company 15 years ago.
=================================================
Forgive me if my electrical terminology is a bit off.
What do you guys think?
Yours gratefully.
Last edited:
I think that one of the bonded services ( most likely the incoming water supply ) has a very low impedance to Ground and that a small voltage difference between the MET and Ground is driving a significant current through the bond.
Provided the Network Neutral conductor is continuous from the MET to the Neutral Terminal at the substation and the local loading on the three phases is reasonably well balanced then the potential difference between MET and Ground will only be a few volts and the current in the bond from MET to ground will be a few amps at most. The low impedance to Ground is an advantage in this situation.
If there is a fault ( Neutral open circuit ) or serious load un-balance that drives the incoming Neutral potential well above Ground potential then the current in the bond wire will be large. The circuit from MET to Ground via the bonding has no fuse or protective device in the property. Neither can it be disconnected in the property. In worse case situations the current in the bond could be hundreds of amps. In this situation the low impendance to Ground can create the hazards of damage due to the high currents in the bond cable.
The worst case is a metal water supply pipe and cable damage in the network that raises the network Neutral to a high voltage above Ground.
A broken Neutral will result in the local network neutral current going via the bond and ground to the substation.
A Phase to Neutral short in the network will create very high currents in the bond cable limited with only the 200 or 800 amp fuse at the substation limiting the current.
That is what I think.
You've two choices here really. Leave things as they are and stop worrying about it, or have the electricity supply completely removed from your house and use candles as your source of heating / lighting.
How much currently flowed through the bonding cable in that situation would obviously depend on the location of the short - the closer it was to the substation, the greater would be the proportion of the current which returned to the substation through the neutral. However, in such a scenario I would expect the substation fuse to operate very quickly, anyway.
Kind Regards, John
" I " said:
That was assuming the fault that caused the Phase to Neutral short had also severed the Neutral between fault location and substation.
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We already have found a solution so we can live in the house, by having the downstairs ring main off all the time. As for heat, we have gas central heating which is now running off the upstairs ring main, and we unplug that now when we don't need it. The house is feeling alot better with the downstairs ring main off, like a massive health improvement for us all.
After completing the checks on the ring main, socket 1 shows higher readings. I went to remove it, and the cables were to short to inspect. Ive since this morning removed the boxing that was surrounding the pipes and original socket1. I found that the handy men had made a boxing for the pipes, moving the socket front to the front of the boxing, but leaving the wires exposed and the original back 2gang behind it by about 2 inches.
This socket also has an unfused spur running from it to under the counter, and even worse, later another person has tried to add another socket higher above where the cupboard was, but couldnt reach socket1, so they cut the ring and wired 1gang socket. Its not even screwed to the wall, it was sitting on top of the cupboard. This is all at the beginning of the ring in the kitchen, and could be adding to current flow problems im inspecting.
Some people would just sell the house, and leave it on someone else's shoulders. Im not worried as in panic, but i am concerned enough and dedicated to try fix the issue instead of kicking it down the road, like we did the last 5 years.
The mains supply is a complicated issue, i don't think it a neutral & earth short, but it might be worth the distribution doing some checks on the network. It could be something they haven't noticed, and it might be simple issue for them. I know its not cheap, but if we can not sort it, then i will investigate having the earthing switched to a TT configuration.
As for my house, we trying to get a number of tasks fixed & sorted, but keep finding areas out of sight that are concerning. After inspecting the electrics, there is enough evidence to show that the downstair ring main overdue on a health check, and possibly a re-wire at extreme. Ive not finished inspecting all the sockets and the wiring under the floors, but im wondering if it would be ready to certified.
ElectricsRanger
After completing the checks on the ring main, socket 1 shows higher readings. I went to remove it, and the cables were to short to inspect. Ive since this morning removed the boxing that was surrounding the pipes and original socket1. I found that the handy men had made a boxing for the pipes, moving the socket front to the front of the boxing, but leaving the wires exposed and the original back 2gang behind it by about 2 inches.
This socket also has an unfused spur running from it to under the counter, and even worse, later another person has tried to add another socket higher above where the cupboard was, but couldnt reach socket1, so they cut the ring and wired 1gang socket. Its not even screwed to the wall, it was sitting on top of the cupboard. This is all at the beginning of the ring in the kitchen, and could be adding to current flow problems im inspecting.
Some people would just sell the house, and leave it on someone else's shoulders. Im not worried as in panic, but i am concerned enough and dedicated to try fix the issue instead of kicking it down the road, like we did the last 5 years.
The mains supply is a complicated issue, i don't think it a neutral & earth short, but it might be worth the distribution doing some checks on the network. It could be something they haven't noticed, and it might be simple issue for them. I know its not cheap, but if we can not sort it, then i will investigate having the earthing switched to a TT configuration.
As for my house, we trying to get a number of tasks fixed & sorted, but keep finding areas out of sight that are concerning. After inspecting the electrics, there is enough evidence to show that the downstair ring main overdue on a health check, and possibly a re-wire at extreme. Ive not finished inspecting all the sockets and the wiring under the floors, but im wondering if it would be ready to certified.
ElectricsRanger
Assume a twin cable with a live wire and a neutral wire. What ever load is being supplied by this cable the current in the Live will be the same as in the Neutral but in the opposite direction. ( there may be an insignificant difference when the wires are those in a cable that is part of a ring main ) Puttting the sensor right next to one wire would give the magnetic field from that wire. The adjacent wire will have a similar magnetic field but in the opposite polarity. The two will strat to cancel each other out when the sensor is moved a few centimetres from the cable.
The effect of domestic magnetic fields on the human body is in doubt.
http://www.who.int/peh-emf/publications/facts/fs322/en/
When working in the radio communications industry in the 1980's I was aware of several attempts to prove that magnetic fields had a detrimental effect on health. None of the "proof" could be validated. The effect of radio frequency energy on flesh was a known hazard when standing close to a powerful transmitter. But magnetic fields of a few milli Tesla were never proven to be harmful. ( But that could be wrong )
Small but there have in the past few years been several instances of bond cables melting.. and the probability of that occurring is?
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