help with a supply problem. TT split phase

[fletchflash]

Hi all need a bit of help with a remidial from one of my PIR's.

Its from a PIR at a carehome.

One of the defects is the supply from the cutout to the main DB.

TT system, split phase. The main DB is about 10metres away from the cutout, which is in a meter box on an o/s wall. The supply is run as three seperate 25mm singles (L1,L2,N) up a wall void and then above a kitchen ceiling. The earth rod is about 2 foot away from the meter box then runs up the wall and across kitchen ceiling to DB, not entering meter box.

Tis all a bit of a mess, all 3 cables look real tatty, like someones had a hard time dragging them through the wall. Theres no fused isolator, no RCD protecting the meter tails.

I intend to replace this supply with a 3 core swa, fed from a 100mA time delayed RCD and isolation within the meter box.

Whats anyones thoughts on this?

Im not entirely sure on best way to acheive everything, DNO required isolater for length of tails, RCD for cable to meet disconnection times etc etc. Room is tight within the meter box.

to top it all off, its not technically a split phase. everything installed is as a split phase supply (main DB, warning signs etc). But after the cutout one of the phases is disconnected (fuse still in) and a single phase meter installed onto L1, then into a henley block, splitting into two 25mm2 cables (marked L1 & L2). This makes me think a meter change may have been done in the past few years, the person changing it only putting it onto one phase. I intend to speak to the DNO about it tommorow as its a bit too much load for single phase, its a 40 room carehome with kitchen, laundry etc.

Anyones views would be much appreciated, apologies if its drabble is quite alot of details to try and cram in.

Cheers

 

[steptoe]

sounds like an old 2phase supply and the meter monkey didnt understand this, only ever saw single ph or phoned head office to ask for a 3ph guy to be sent out,

can you test across the other phase to determine if it actually is another phase or not, or simply a dual fused supply.

 

[Sidewinder]

Fect,

Could "have" been a summation supply?

As Steps says, meter monkey had no idea of what he saw?

You should really check out your (our) side and make sure it is OK, their side is their side, and is their responsibility really.

 

[fletchflash]

my exact thoughts were also a meter mans mistake. He's also left a small amount of copper showing from neutral at bottom of meter. I'll put a photo of the meter box on tommorow, but theres a gap where the small plastic knockout from the second fuse has been removed, like there used to be a cable there. There was gap big enough to get a probe in and it tests out as a phase, 480v between L1&L2.

I know its there responsibilty for there side, but if meter monkey has put all load on one 100a phase? ive flagged it on a PIR and told manager it needs sorting, im gonna ring DNO tommorow and ask them, will let you know what they say.

any thoughts with the supply, supposing i do get it restored to split phase?

 

[steptoe]

its not split phase if you are getting >400v , its a 2ph supply.

 

[fletchflash]

its not split phase if you are getting >400v , its a 2ph supply.

why?

 

[steptoe]

if it was a single phase the there would be no difference in potential between line and line, so it must be L1 & L2 to give 400v potential, can you show us a pic?

 

[fletchflash]

steptoe you're confusing me mate!

Perhaps I'm not being clear enough on the details. Ive measured 480 volts L1-L2 at the service head before the meter, managed to get a probe in to where L2 should be connected and to L1.

the single phase meter is connected to L1. After the meter the supply splits at a henly block, but the two cables are supplied from same phase.

I will put a pic on tmrw when im on my other computer

thanks for help

 

[steptoe]

fletch, you are being clear, Im not, Im rubbish at this,

you have by the looks of things so far, a 2ph supply,

your meter monkey, having never seen this before has assumede single phase with 2 fuses, so has disconnected ph2 and gave you one supply on 1 ph,

you need to check if you are still being billed for 2 phases?

you need to get them to re-instate the 2nd phase.

I dont know how England works, but lots of DNOs dont like providing 2phase supplies any more.

 

[Riggy]

Steptoe, OP is correct. Split phase 480V between "phases", two phase 415V surely?

 

[fletchflash]

heres a pic or 2

As you can see certainly looks like a meter change done incorrectly.

Ringing the DNO today, Im also trying to get hold of a test done by a 3rd party logging the power usage of the building. will post what happens later

 

[Andy™]

fletch, you are being clear, Im not, Im rubbish at this,you have by the looks of things so far, a 2ph supply,

your meter monkey, having never seen this before has assumede single phase with 2 fuses, so has disconnected ph2 and gave you one supply on 1 ph,

you need to check if you are still being billed for 2 phases?

you need to get them to re-instate the 2nd phase.

I dont know how England works, but lots of DNOs dont like providing 2phase supplies any more.

split phase is common in rural areas. only need 2 conductors to a small village etc instead of 3

 

[m4tty]

Am I missing the point here (can someone explain to me if I am) but isn't that a 3 phase head using phase 1 and neutral and the single phase has been Henley blocked and 2 feeds taken from there?

 

[Sidewinder]

m4tty there is a difference between split phase and 2 phases of a 3 phase supply.

There are terminal voltage differences, and the phase shift is different, but off the top of my head I can't remember the details, the voltages quoted in the thread seem right though.

 

[Manator]

Your correct Matty, the problem may be that as the other posters have said, the meter monkey did not connect two meters, and decided to cut the other one out. My opinion, is that it looks like a right amateur job, and I doubt it was originally supplied or left like this.

 

[Andy™]

Am I missing the point here (can someone explain to me if I am) but isn't that a 3 phase head using phase 1 and neutral and the single phase has been Henley blocked and 2 feeds taken from there?

split phase is 180

 

[Riggy]

Best way (for me at least) to think of split phase is like a centre tapped 110V site transformer, but at 460V. i.e. it's single phase, transformed to 460V then centre tapped to give 2 x 230V feeds, one each side of the centre tap (which is the neutral for both halves).

I've seen a DNO guy put his phase rotation meter onto a split phase supply before, then look totally confused when it registered.....................nowt!

 

[steptoe]

Steptoe, OP is correct. Split phase 480V between "phases", two phase 415V surely?

415 would be across 2 ph of a 3ph supply,

not 2 ph of a 2ph supply,

maybe I just call stuff different. :C

the problem I have now is,

it just looks like 1 ph being used?

is the Neutral at a potential to earth??????

 

[Sidewinder]

No Steps it would be 400V across 2ph of a 3ph supply regardless of what you actually measure]

Split phase is something different again.

 

[steptoe]

oh, thats right, cos the DNO changed all the TXs in 2008, so we get 230v now.