High PFC

[bearlyable]

Hi all advice is greatly welcome

I originally had reading of PSCC 19kA until I returned my meter to Megger who have sent it back repaired and recalibrated.
I have a high PSCC 7.2kA this is on a TN-S system there is a sub station about 340 metres away CU is a wylex dual RCD jobby the breakers have a breaking capacity of 6kA.
Mains fuse is a BS 1361 Type II
The PEFC is below 4kA
and Ze =0.05 ohms
The actually question is what shouid I do
Do I need to replace all CU components to accomadate this current ie above 6kA breaking capacity.

I appreciate any advice all knowledge is an improvement

 

[zupos40]

What type of installation, is it new housing etc

 

[bearlyable]

It a Victorian terrace, original install probably 15 years old

 

[zupos40]

It a Victorian terrace, original install probably 15 years old

Then I would replace the All the cbs if possible with 10 KA, why I asked that mates have started new housing estate with 30+ properties where when the first house was tested the PFCexceeded 10KA, but as the other houses where being completed the PFC came down as the load increased and when inital house was tested it went down to under 2kA.

What was the supply voltage at time of testing, the only other thing I can thing of doing as retest using another meter, the OSG 57 states that domestic installation prospective fault current is unlikely to exceed 6kA.

Personally I never recorded PFC more 4.2kA on domestic properties, normally 800A to about 2kA is what I observe.

BS 1361 is ok at it rated to 16.5kA

You could try contacting the technical dept of local supply autherity.

 

[bearlyable]

Voltage read 248v

 

[zupos40]

Voltage read 248v

I only asked because, I known REC to alter the transformer winding (overtapping) etc (normally when voltage is low), so I thought if it was high may be that what they may have done.

I still think it worth contacting them they may have replaced the local transformer or altered it for some future expansion any new properties being built locally.

If so when the extra load goes on impendance may change and PFC comes down.

If you contact technical would you let us know what they say or what solution you decide on.

 

[mechelec]

As i understand it the cutout fuse willl be the only protective device to see the full PSCC and these are good for 50KA (BS88type 2 @400V) the circuits within the property all have an impedence that will limit the PSCC that the circuit breakers will see to acceptable levels???????
Please feel free to correct me.

 

[bearlyable]

Their coming to resecure the cut out as its in a cellar and the wall is damp causing the cut out board to be falling off.
Ill get them to do a reading then if that still shows high they should tell me then why. I will try to remember to give you the results in the meantime thanks very much for your input into this issue the comments about new build was very interesting and would be invaluable knowledge/experience for the future so once again thank you very much all knowledge is advancement so cheers

 

[zupos40]

As i understand it the cutout fuse willl be the only protective device to see the full PSCC and these are good for 50KA (BS88type 2 @400V) the circuits within the property all have an impedence that will limit the PSCC that the circuit breakers will see to acceptable levels???????
Please feel free to correct me.

Yes but cutout fuse is BS1361 in this case and single phase, I not sure fuse will limit PSCC, what is an acceptable level.

 

[Mr Mark Sparks]

- 434.5.1, P76

have a look at this reg its to do with the cut out fuse holding the fault so that your high reading at the cu complys

not got regs to hand but found it in another similar thread

 

[zupos40]

- 434.5.1, P76

have a look at this reg its to do with the cut out fuse holding the fault so that your high reading at the cu complys

not got regs to hand but found it in another similar thread

Reg states a lower breaking capacity is permitted if another protective device or device having the necessary rated short-circuit capacity is installed on the supply side. In this situation , the characteristics of the devices shall be co-ordinated so that the energy let through (I squared t) of these devices does not exceed that which can be withstood, without damage, by the device(s) on the load side.

I believe the pre acring I squared T min = 22 A's
max = 42 A's

I do know that most 6Ka Cb to BSEN 60898 I squared t max is 29700 A's so not sure it does comply, also unsure what Isquaredt is for old BS3871

Finally where I live the REC removed there main fuse and replaced it with a link (pre 1981), The only protective is 300A MCCB in the basement, how i know they updated my electricity meter about 3 years ago.

Hi all advice is greatly welcome

I originally had reading of PSCC 19kA until I returned my meter to Megger who have sent it back repaired and recalibrated.
I have a high PSCC 7.2kA this is on a TN-S system there is a sub station about 340 metres away CU is a wylex dual RCD jobby the breakers have a breaking capacity of 6kA.
Mains fuse is a BS 1361 Type II
The PEFC is below 4kA
and Ze =0.05 ohms
The actually question is what shouid I do
Do I need to replace all CU components to accomadate this current ie above 6kA breaking capacity.

I appreciate any advice all knowledge is an improvement

I have been surfing the web and It seems that if your domestic installation CCU complies with BSEN 60439-3:1991 (and it seems most manufacturers do) and the ccu is protected by Bs1361 Type II upto 100A then the board and protective device are ok up to 16KA (do not matter whether the cb are 6kA, 10kA or 16kA).

So in answer to your enquiry it seem you do not need to do any thing just put your results on the test sheet on to the next adventure.

I learnt something new today as well.

 

[mechelec]

Very usefull answer zupos40

 

[bearlyable]

Tar Fut dat chaps.