What would happen if....

[Hugh Jaleak]

A neutral was connected to earth? I've been trying to help out here:
http://www.diynot.com/forums/viewtopic.php?t=203411
Im not professing to understand the theory behind electrics, but surely the neutral needs to be connected to a neutral at both ends here?

 

[Spark123]

Firstly if a circuit has a N-E fault on it and it is on an RCD it will either keep tripping it or trip it when load is applied, possibly a load on another circuit. These symptoms depend on supply type.
Secondly should there be an open circuit neutral fault somewhere the N-E connection can act as the return path and lots of current can flow through the wires of the circuit overloading them.
It is also illegal for a consumer to use a protective conductor as neutral.
Neutral (and Line/Phase) are classed as a Live conductors and must only be used as such, a neutral cannot be used as a protective conductor (unless you have permission from the secretary of state like the DNOs.)

 

[Hugh Jaleak]

Thankyou, although I wont profess to understand some of your reply! My concern was the OP in the plumbing section was trying to get his new stat to work, whilst its easy to connect the neutral at the stat end, I was concerned it should also be connected to neutral at the other end. Simply tying an existing wire into a neutral connection without ascertaining its origin at the other end of the cable seemed a recipe for trouble to me. Whilst it may work it doesnt follow thats its either legal or safe......

 

[Spark123]

If they went to the trouble of installing a 3c+e cable for a stat I'd hope they had connected one of the cores to neutral, one to phase, one to switch live and the bare one to earth.

 

[ericmark]

I must admit I was suppressed at the advice given. Fools rush in where angles fear to tread.

1) Blue or black should not be automatically assumed as neutrals according to age they could be phase wires and where blue is with red and yellow or black is with brown and grey one should not assume they are neutral.
2) On single phase supplies all line wires should be red or brown according to age of installation and where three phase colours are used then the other two colours should have sleeves.
3) Because in the case being talked about there is no standard colour code to try to tell anyone:-
Red = 1
Blue = 2
Yellow = 3
Is crazy. Honeywell do give those colours on their guide 104 but there is no way of knowing if the person wiring the unit has even seen that guide.

The Honeywell 6360B on Screwfix site does have the instructions showing 5 terminals Earth, 1 = Common, 2 = Resistor (Neutral), 3 = Heating load, 4 = Cooling load. No colours are suggested. At £19.99 with Horstmann starting at £7.49 it is expensive and for £23.25 a unit which does not require a neutral and has a timer combined is available.

However you are still back to no idea how it is wired as no photos of boiler or programmer so no idea what red, yellow and blue have been used for.

The neutral on the old bi-metal thermostats reduced the gap between on temperature and off temperature and if not connected at all the thermostat would still work. And often I have found it disconnected and only two wires are used.

So no short cut only way is to test or trace. No one can give the colours at best a guess and at worst darn dangerous.

 

[Steve]

I was working on a circuit in my shed yesterday. I had isolated its individual MCB (6A for lighting). Neutral still connected. The 32A RCBO in the shed feeding the sockets was on, because the tumble dryer was working. I would have flipped the main isolator in the shed if it werent for this. The whole setup is RCD protected from the house end (on a split load).

As I removed a floodlight, its three cores touched, neutral and earth. The RCD in the house tripped. (I actually heard a slight click when the two touched, and the dryer stopped without its internal relays clicking) I'm not sure if distance is a factor here, the tumble dryer - a heavy load, being close to where I was working.

Working on the circuit today, I dropped its neutral out of the board.

 

[Hugh Jaleak]

Thanks to all who contributed. (Im not usually up at this hour, but man flu has led to a barking cough, (smoking dont help-I know!), and the TV is rubbish). My concern was if the OP was to connect up at the stat basically using guesswork, without ascertaining where how other end was connected, he could have produced a possibly dangerous situation.