Line and neutral same size?

[La Poste]

Greetings.

I will probably get shot down in flames for asking this but...

If you are wiring something in singles and you are getting low on 1.5mm cable but have plenty of 2.5mm cable left would it be acceptable to run your neutral in 2.5mm even if the line is 1.5mm?

The circuit is protected by a 6 Amp MCB, a standard lighting circuit.

I have had a look at the Regs number 524.2 and it states "the neutral conductor shall have a cross sectional area not less than the line conductor". Which in this case the neutral will be bigger than the line conductor so definitely not less.

I know it sounds a bit cheap skate but in this day and age we are always looking to save costs and keep the price of the job down.

Does this seem really unprofessional to you, I mean at the end of the day the reason I'm considering doing this is to save the customer money.

Thanks.

 

[Amp David]

If i was to see i'd think whats going on here!
A roll of singles isn't that much.

Yes to me I'd be thinking lazy more than unprofessional

 

[johnboy6083]

Agree with amp David. It would confuse anybody coming after you! If your running low on 1.5 and have lots of 2.5, then run the whole lot on the bigger stuff.

 

[La Poste]

Agree with amp David. It would confuse anybody coming after you! If your running low on 1.5 and have lots of 2.5, then run the whole lot on the bigger stuff.

Aye that will be the one.

Thanks a lot.

 

[Amp David]

And not being a lazyboy!!! ha ha

 

[ackbarthestar]

Its better than the other way, where the neutral has been reduced due to an original spec supplying lots of 3 phase equipment and then removed and replaced with equipment that has both 4 pole and single phase equipment installed !

Yes I know that would be applied to sub-mains and not final circuits.

 

[Engineer54]

Its better than the other way, where the neutral has been reduced due to an original spec supplying lots of 3 phase equipment and then removed and replaced with equipment that has both 4 pole and single phase equipment installed !

Yes I know that would be applied to sub-mains and not final circuits. unless its single phase lighting spread across 3 phases and the neutral is shared between the phases

I hope not!! Each circuit would be made up of a neutral conductor of equal size to the line conductor.

What your describing, is what the Yanks call a ''multi branch circuit'' where all the branch circuits run off a single neutral conductor that supplies all phase line conductors.
A perfect way to overload the neutral conductor, where inductive lighting loads, make up those circuits!!

 

[ackbarthestar]

I hope not!! Each circuit would be made up of a neutral conductor of equal size to the line conductor.

What your describing, is what the Yanks call a ''multi branch circuit'' where all the branch circuits run off a single neutral conductor that supplies all phase line conductors.
A perfect way to overload the neutral conductor, where inductive lighting loads, make up those circuits!!

Its unlikely that 3-phase lighting will suffer that much since each phase is, as said, out of phase by 6.67ms and will be able to cope.

Its standard practice to reduce the size of the neutral in this country, although needs careful design, where most of the loads are balanced

 

[La Poste]

Harmonic currents seem to be a bigger issue in the Regs these days.

Especially on a three phase neutral.

I hear they can get quite high.

 

[Engineer54]

Its unlikely that 3-phase lighting will suffer that much since each phase is, as said, out of phase by 6.67ms and will be able to cope.

Its standard practice to reduce the size of the neutral in this country, although needs careful design, where most of the loads are balanced

When your taking the return currents of inductive lighting loads of any size, that single neutral conductor starts looking susceptible, add any unbalance, even more so!! Do they still allow a single neutral conductor as the sole return path across 3 phases on inductive lighting circuits in the Reg's??

Not so much used these day's, they are increasingly feeling the effects of harmonics and whatever... I never did like these reduced neutral supply cables, and never used them, except where a neutral was required, but not in the sense of load requirement. ...ie, control and monitoring circuitry etc...

 

[ackbarthestar]

When your taking the return currents of inductive lighting loads of any size, that single neutral conductor starts looking susceptible, add any unbalance, even more so!! Do they still allow a single neutral conductor as the sole return path across 3 phases on inductive lighting circuits in the Reg's??

Not so much used these day's, they are increasingly feeling the effects of harmonics and whatever... I never did like these reduced neutral supply cables, and never used them, except where a neutral was required, but not in the sense of load requirement. ...ie, control and monitoring circuitry etc...

I think the regs still allow single neutrals on '3-phase' lighting 559.6.2.3, but as I said requires careful design!

 

[Knobhead]

Some American cable manufacturers are now making cables with 1½ X neutral conductors due to the problems with harmonics.

 

[Engineer54]

The use of those reduced neutral cables were always a bit of a folly. They are fine with conventional loads that are substantially balanced, and won't be added too in the future. But there lies the problem with them, they were extensively used willy nilly to reduce costs, with little or no forethought to future extensions, or the now common use of inverter type motor controls and the like.

Now your seeing a lot of these main and sub-main reduced neutral cables being replaced with full sized cables. I've seen some horrendous consequences where these cables have been utilised in the wrong circumstances just to save on initial installation costs.

 

[ackbarthestar]

The use of those reduced neutral cables were always a bit of a folly. They are fine with conventional loads that are substantially balanced, and won't be added too in the future. But there lies the problem with them, they were extensively used willy nilly to reduce costs, with little or no forethought to future extensions, or the now common use of inverter type motor controls and the like.

Now your seeing a lot of these main and sub-main reduced neutral cables being replaced with full sized cables. I've seen some horrendous consequences where these cables have been utilised in the wrong circumstances just to save on initial installation costs.

Well until the regs change, I suppose like BS3036 semi-enclosed protective devices, they will continue to be permitted in installations. Whether or not this is aimed at existing installations or for new ones remains to be seen. Personally I wouldn't be too happy with reduced sized neutrals for many high frequency switching applications.

 

[Chr!s]

Greetings.

I will probably get shot down in flames for asking this but...

If you are wiring something in singles and you are getting low on 1.5mm cable but have plenty of 2.5mm cable left would it be acceptable to run your neutral in 2.5mm even if the line is 1.5mm?

The circuit is protected by a 6 Amp MCB, a standard lighting circuit.

I have had a look at the Regs number 524.2 and it states "the neutral conductor shall have a cross sectional area not less than the line conductor". Which in this case the neutral will be bigger than the line conductor so definitely not less.

I know it sounds a bit cheap skate but in this day and age we are always looking to save costs and keep the price of the job down.

Does this seem really unprofessional to you, I mean at the end of the day the reason I'm considering doing this is to save the customer money.

Thanks.

It will help your volt drop

 

[ackbarthestar]

It will certainly give the next sparkie on site something to think about !

 

[Chr!s]

Well until the regs change, I suppose like BS3036 semi-enclosed protective devices, they will continue to be permitted in installations. Whether or not this is aimed at existing installations or for new ones remains to be seen. Personally I wouldn't be too happy with reduced sized neutrals for many high frequency switching applications.

Well to comply with the regs its not that straight forward , if you have not assessed the loads including any harmonics and that neutral is not protected then this would be a departure from BS7671.

 

[ackbarthestar]

Well to comply with the regs its not that straight forward , if you have not assessed the loads including any harmonics and that neutral is not protected then this would be a departure from BS7671.

Who said that it was? - bun fight?

Merry Christmas