E7 Neutral Switching

[davetheglitz]

Hi - just been dealing with a 3 phase dual rate digital meter - and the control wire for E7 is switched to neutral to activate the E7 contactor. Surely this is not to BS7671!  Anyone had any experience of this?

 

[loonytoon]

Yes. Recently had a property where the old meter was neutral switching to 3 contactors feeding 3 flats night storage heaters.

G4S came in and fitted new 3p meter which just switched outputs of meter thus rendering contactors useless.

Took several visits and phone calls to G4S, British Gas and SEB to find out why they weren't working, to find out old meter was neutral switching and G4S monkey had just stuck it in without checking.

 

[Sidewinder]

OK, but N switching!

For pity's sakes...

 

[loonytoon]

I know, but then the original install is 1960's, so guess it was the norm then.

Its only a small fire wire which came from the old E7 time clock, so no loading as such, but agreed, why neutral?

That's the electricity board for you though, make there own rules up, and as its 'their side', not my problem.

 

[SLIPSHOD & SLAPDASH]

I found this out last year when replacing a landlords 3ph meter. Had to  phone the meter  supplier as i  couldn't work it out and no instructions were supplied . I suppose until fairly recently this would not have been under BS7671 as it would have been on the supply side.

Most electronics switch the neutral (or negative) so i guess thats where this comes from ?

 

[SPECIAL LOCATION]

If I recall correctly a lot of bathroom timer fans do actually switch the neutral to trigger the fan...

Guinness

 

[steptoe]

ok, so ELV, but dont alarms switch the N [0v] for the bell box?

 

[Sidewinder]

BS EN 60204-1 still has some excellent examples why switching an earthed live conductor is a bad idea!

 

[Andy™]

If I recall correctly a lot of bathroom timer fans do actually switch the neutral to trigger the fan...

Guinness

correct. at least with manrose fans anyway. you can see the perm live connection runs stright to the fan connection at the other end of the board

 

[Evans Electric]

As Slippery said above ,  metering is not covered by 7671 ,  but are you saying it is now ?   

 

[SLIPSHOD & SLAPDASH]

As Slippery said above ,  metering is not covered by 7671 ,  but are you saying it is now ?   

One example, We look after an industrial site sub divided into about 30 units each with a landlords 3 phase duel rate meter.  There is 3 EDF supplies into the complex