How To Reduce Voltage Between Neutral And Earth
- #1
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Hi
I recently had a PV system we installed switched off after the Electrical Contractor got a shock off the Neutral. He was wiring lighting only after a processes of elimination found the error was on our PV circuit.
We did expressionless tests on the circuit
Insulation resistance (1000v)
Continuity
Polarity
Merely no faults came upwards. He would not permit us re connect information technology until the fault was found. Now the question:
He would let us connect the live but not the neutral (in case it livens up all the neutrals and earths in the school), so alive and globe was connected to their DB). Nosotros disconnected the PV organisation so nosotros just had a 20m 3 core flex from plant room to roof. When the live was connected to he live DB nosotros would get 104v across neutral (not connected to DB and earth (connected to the DB)
When the micro-inverters were connected we would become 240v across earth to neutral.
When nosotros finally continued the neutral to the DB the voltage betwixt world and neutral dropped to 1v.
Anyone shed any light on this? Happy to give more info if it's not clear but it'due south a long mail already.
Thanks people
- #2
I very much dubiety in that location was a fault on your installation which was causing the electrician working on lighting circuits to get a shock from a neutral.
How did he decide the fault was on the PV installation?
Telling y'all to connect the live and cpc of your circuit and non the neutral is unsafe and absolutely pointless as an energised circuit with the neutral asunder will give you lot a voltage on the neutral if there is something on the circuit switched on, as you found out!
- #3
I was going to make a comment but I'm completely confused most several things to be honest.
What's the earthing organisation of the installation?
- #4
Aye,there is a host of details required,hither...non least of all,what instrument was used to measure the voltage.
- #5
My guess would be in that location is a small-scale leakage electric current flowing in the world line, because when he took the starting time measurement this system was Non grounded properly, so this current had no where to go. So it took the path thru the chief bond and up the neutral line.Once the arrangement was grounded properly, this modest leakage current will bleed off thru the ground.
- #6
Thank you for the comments and then far. Happy to give more item:
Earthing: PME
Testers: Fluke Multi-office and Ethos Multi-meter
How he decided it was a mistake on my circuit:He spent awhile disconnecting each lighting circuit, then switched off each MCB, my circuit was one of the concluding.
When you say the system was not grounded properly, do you lot mean my circuit or all circuits. My first fault finding was to go over all my connections and visually audit the cables and all was perfect. If you mean the whole installation, he did the same on his DB.
- #8
Yea either nosotros dont have every detail hither or the "electrician" didnt know what he was doing
- #9
Focus people. I'chiliad request a specific electrical question non asking for judgment. If at that place are gaps in the explainstion then show your experience and ask specific questions.
Murdoch- re read the OP. He switched off the circuit
Suffolkspark: Re read the last line of the OP. Happy to give more than info. What would y'all similar to know?
- #ten
I'k thinking peradventure a wiring polarity fault in that circuit or problem with floating North?
Related idea - TNCS system has N and E solidly connected at the cutout. Verify. Then I'd be using wander lead to see what'due south really connected to what, equally large N-E voltages shouldn't happen.
- #11
Wilko, yes we went through all that. The Electrical contractor idea it might be to do with the LPS.
But floating Neutral seems to exist the key word here. I found a great article explaining it
IET Forums - Floating neutral? - https://www.------.org/forums/forum/messageview.cfm?catid=205&threadid=103200
I'chiliad thinking
i) The initial Neutral fault on the system wasn't from our circuit afterwards all
2) Equally Streamer mentions, our testing procedure was flawed by dis-connecting the neutral (and creating a floating neutral). I didn't recollect that, by dis-connecting the neutral of a cable (even when not continued to a load) would hateful I would get a voltage reading from neutral to earth when the live of that cable is connected.
I call back I've been nicely schooled hither, simply still open to other comments/opinions on this.
- #12
how do y'all know there wasn't a load connected? any load however small will make the N of the circuit "live" if Northward is not reliably connected back to source.
- #thirteen
We can't exercise an insulation resistance test on the micro-inverters then the cable was dis-connected and terminated in a connector block.
- #15
Indeed I am. Does this mean you will now give a more technical response than your last ii posts?
- #16
The neutral conductor volition only exist neutral whilst connected to the neutral signal of the supply, once it is disconnected from the neutral point information technology becomes just another usher and volition behave as such.
So if it is connected (via a load or fault) to a live usher is volition be at that potential with reference to earth or the neutral point. If it is not connected to anything just is in close proximity to live conductors it will have a capacitively coupled voltage on information technology which could be anything up to the full potential of the live conductors.
- #17
For the neutral of the lighting circuit to be live and give the electrician a shock information technology must have been asunder from the neutral indicate of the supply assuasive it to rise to a live potential.
This suggests either a borrowed neutral or incorrect isolation of the circuit.
If a calorie-free is switched off via the switch and non the MCB and then all other lights on the excursion volition still be using that neutral, so if the neutral is broken at the low-cal being worked on one of the ends will become live. As an apprentice I did this exact thing on a lighting excursion in a conduit system.
- #xviii
That is a far more than eloquent way of maxim what I was trying to say and makes far more than sense!
- #nineteen
Hello bud,what i am focusing on,is that yous may not have used the correct instrument,to determine the nature of those voltages.
- #twenty
So y'all asunder the neutral into a choc cake then tested from the N in choc cake to earth and wondering why you got 240v??
- #21
I day someone will come with a procedure that could be named "safe isolation" 
It may very well reduce the chances of people getting bumps
- #22
That wasn't directed at you lot. Pitiful if I wasn't clear. Me and the guys in the company have a express mirth almost the Merchandise Forum version of Godwin's police force. "How many posts until the inevitable accusation of not being a 18-carat sparks/plumber/engineer etc"
- #23
Thanks mate. I'm actually glad you could really empathise my question. The capacitance of the disconnected neutral is the respond. I knew information technology was a flaw in the testing procedure just as I couldn't explain it like you lot I couldn't purseude the main electrical contractor.
- #24
Thanks once more everyone who posted. I actually appreciate being able to get to the bottom of this.
- #26
No. He just explained the faulty examination procedure I was doing which gave the voltage reading on neutral even once everything was disconnected.
The original error which caused the stupor would well-nigh likely have been a loose neutral somewhere on the circuit. This was corrected even if nosotros never establish exactly which cable was loose. The isolator is four pole, then possibly the neutral switch didn't connect properly when starting time switched on. The excursion was fully tested 3-iv times and what could be inverse was, so I'm comfortable that the fault is no longer on the excursion.
Source: https://www.electriciansforums.net/threads/voltage-across-neutral-to-earth.159660/
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