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Discuss Split Phase supplies in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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a1colly

Regular EF Member
Hi all

Hopefully somebody will be able to help out a confused idiot!

Visited a farm today which has recently had a supply upgrade from signle phase to split phase, thought I'd have a quick look at what had been done and noticed that they had bought the new supply cable in and added a new cut out to the side of the existing one.

This then gave them the two phases but also two neutral's. I was under the impression that its usually just 3 core's with there being only one neutral.

Is there any reason for this being done in this fasion, would they have combined the two neutrals withn the junction point below the meter and connected a single line in or would they both be connected through the meter?

Would they have any need to have the second neutral conneted at all or would this just be terminated?

I know alot of questions but thanks in advance.
 
K

Knobhead

Are there going to be any 460V loads? If not just treat it a 2 supplies. Have the DNO linked the two neutrals? Can you post pictures of the service head?
Sorry but there’s lots of questions you need to answer so we are not guessing.
 

micknew

Electrician's Arms
Supplies are normally single phase 230V or 3 phase 400V.
If split phase or 2 phase voltage would still be 400V between phases and 230V phase to earth.
The above applies if the supplies come from the same transformer of course.
Confusing.
 
Last edited:

IQ Electrical

Electrician's Arms
No, if it's split phase or 1 phase 2-wire, voltage between phases will be 460 Volts. I've tested many of these supplies and never seen a second neutral, strange!
 
K

Knobhead

Without any input from our OP it’s all guess work.
But as you say IQ it sounds a weird set up.
 

a1colly

Regular EF Member
Hi all

Thanks for the input. I've been back to the site tonight, a little more information for you.

The split phase was put in for a future PV instalation 16.7KW system across the two phases.
I have removed a few seals and discovered that the live and neutral of the second phase are wired up and are currently feeding a single phase CU. The live and neutral of the first phase are connected to the supply and load of the first phase connections on the meter with an isolater fitted on the neutral connection to break the circuit.

I have called the DNO to have them alter the connections for the PV company in advance and to allow me to complete some alterations to the CU. However, I am unsure as to why there are two neutrals supply's and why they have now linked out through the load and supply of the meter.

Thanks
 

MarkRibbands

Regular EF Member
I live in a house with a split-phase supply and have picked up a lot of tips about this rare animal. It was all about saving copper after the war.

Yes, it is 460V phase-to-phase (Of course that’s 480V+ in reality), since it’s only two phases, 180 degrees opposed.

Sorry, Mick – this is NOT two of the usual three phases from a three-phase transformer at 120 degrees.

Why two neutrals? Maybe the DNO run an additional single-core concentric cable for the additional phase, so it was easier to terminate by using a second single-phase service head?

Is it PME? What’s the resistance between the two ‘separate’ neutrals?

Presumably there’s a new three phase meter, wired as 2-phase 3-wire? Or maybe TWO single phase meters – an old one plus a new one?

It’s an interesting one this …

Maybe needs a photo :)
 

a1colly

Regular EF Member
Photos will post tomorrows, new three phase meter fitted hence when removed the tags found the neutral and postive wired into the first phase.

Am hoping the engineer can give me a little insight into it tomorrow aswell when i get the usual tellig off :)
 
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