Max PFC gone through the roof....Ideas anyone?

[Eggster71]

Hows that then, an RCBO CU will be no bigger than the board it's replacing!! Extending existing circuit tails within a new CU is standard practice, so no excuse there to hide behind!! lol!!

Width wise, yes, height wise, problems. Not impossible but as far as the L/L is concerned the circuits have RCD protection and although not ideal he gets a "satisfactory" cert back so why spend another 4-500 if he dosen't need to...His choice, not mine...

The reason you readings are inconsistent is your probably nearly sat on top of the local substation and you have approached the resolution limits of your meters hence the differing readings....

I've tested this property for quite a few years and never had these readings, previously all below 3kA, some "repairs" have been done in the road since last time I tested it. Agreed the >19.9 result is over-range for my tester the other 2, on a seperate phase are both a great deal lower. Same results recorded, give or take a bit on 2 different meters.

 

[Eggster71]

Another option that you might consider is splitting the meter tails via henly blocks, then feeding 3 or more switched fuses with bs 1361 II 40 amp fuses, that in turn feed 4 way boards via 10 mm tails, the smaller feeders to the boards will lower the psc to a value more in spec with protection with bs/en 60898.

It might look like something out of the late 70s with 3 or more switched fuses and boards, but when economy favours over appearance, then compliance is paramount.

Just out of interest what psc are you getting at the first outlet on any circuit when you perform a loop test?

Definately no room to fit all that stuff in mate! TBH, never did a test at first point, closest final CCT loop result was cooker outlet at one flat which came back at approximately 0.35 ohms I think so no real concern there.

 

[Eggster71]

Higher-accuracy low Ze test procedure

Cunning!

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Higher-accuracy low Ze test procedure

Cunning!

 

[chilliwilly]

Definately no room to fit all that stuff in mate! TBH, never did a test at first point, closest final CCT loop result was cooker outlet at one flat which came back at approximately 0.35 ohms I think so no real concern there.

I know its a periodic that you are doing and you've ticked satisfactory, but if it ever arises during an addition or alteration. You could consider using the existing consumer unit as a junction box, and barrel crimp final circuit tails to extend them, then mount a fire rated board in front of it and bring the cables through it to new switch gear.

 

[Norwich]

We have this from time to time when transformer is close by or on site more an issue of the meter. Meggar mft 1500s do it. Readings are not a concern The cut out fuse provides adequate short circuit protection 3ka mcb devices are fine. We have used a long lead to measure the psc and ze and then deduct lead measurement. All to with having low impedance and no resistance metres don't like it

 

[Engineer54]

We have this from time to time when transformer is close by or on site more an issue of the meter. Meggar mft 1500s do it. Readings are not a concern The cut out fuse provides adequate short circuit protection 3ka mcb devices are fine. We have used a long lead to measure the psc and ze and then deduct lead measurement. All to with having low impedance and no resistance metres don't like it

Do they?? ...lol!!

Yep, these Companies only manufacture 6/ 10/ 22 KA MCB's just for show, or maybe just for the hell of it!! Try using that philosophy for a final circuit DB in a sub-station building. ...lol!!!!

 

[Knobhead]

Depending on the size of the transformer the fault level at the terminals would be 29KA for a “DNO standard” 1000KVA transformer. That doesn’t take network impedance in to account, which will drop the fault level considerably. Add the supply cable impedance and you’re down to respectable levels.

From E54’s comment about substation supplies, we never installed MCB’s from the busbars without an intermediate fuse or MCCB.

 

[UKMeterman]

If you get desperate ABB do 25KA MCBs http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/28adfb90da00e772c1257995004b7156/$file/2CCC413003C0202_low.pdf

 

[Engineer54]

Depending on the size of the transformer the fault level at the terminals would be 29KA for a “DNO standard” 1000KVA transformer. That doesn’t take network impedance in to account, which will drop the fault level considerably. Add the supply cable impedance and you’re down to respectable levels.

From E54’s comment about substation supplies, we never installed MCB’s from the busbars without an intermediate fuse or MCCB.

Of course the substations DB would be fed from an MCCB on the switchboard!! lol!! But even up-stream fuses and MCCB's will have a ''let through'' element. If correctly designed, by the time you get to the final circuit DB, you'll be at or around the 20 KA mark. Several manufactures can supply 20 to 25 KA breakers MG, ABB, Siemens etc... They do tend to be much fatter than your standard MCB's mind!! lol!! One thing is for dammed sure, i wouldn't be installing 3 KA MCB's in a sub-stations local lighting and small power DB!! lol!!

 

[chilliwilly]

Has any body actually recorded the pfc/psc between phases? And not just the usual phase to earth/neutral pfc/psc?

 

[Engineer54]

Has any body actually recorded the pfc/psc between phases? And not just the usual phase to earth/neutral pfc/psc?

Always!!

 

[chilliwilly]

Which instrument do you use and what readings do you record?

 

[Engineer54]

Just re-read your post, no i don't ''record'' all those tests, only the highest values!! Not sure what instrument we'll be using on this project, but on previous projects it was either a Megger or Metrel high resolution ELI test kits.

In the past, you had to place a special order for the Megger HR loop tester, but i believe they now direct market such a unit.

 

[Tim]

Mft1730 can measure pfc between phases

 

[Engineer54]

Mft1730 can measure pfc between phases

It probably does, but it's resolution will still be a problem when conducting loop tests near/close to Distribution transformers, which is what were talking about here. Hence the need to use IQs test method or use a HR loop tester.