Excessive PFC Readings (& tiny Neutrals)

[Colport]

Hi all,

Our company recently tested a local factory and I have a couple of questions relating to some of the results obtained.........

The sub station is in the factories car park so we have an extremely low Ze (checked with 3 different meters, all say <0.01 ohms. As a result of this the PSCC/PFC is rather high to say the least (>19.9KA at incomer). The majority of the Distribution Boards are the old MEM M9 type (9KA) but all of the sub main cables are protected by BS88-2 Fuses (80KA). Is it ok to rely on the BS88 fuses to cover the excessive PSCC/PFC readings obtained at the Distribution Boards?

Secondly (hope it`s ok to post two things in one here?), while inspecting the Distribution Boards we discovered that nearly all of the supply Neutrals are far smaller than the phase conductors. The occupants of the factory are not the people the building was originally designed for and there is quite a lot of equipment now requiring Neutral connections (am thinking that originally the Neutral would have been just for local lighting and small power).

Would you agree that we should advise the customer to increase the size of the Neutrals to that of the Phase conductors? (In some cases the Phase conductors are 120mm with a 16mm Neutral conductor).

Many thanks

Colport

 

[Lurch]

Secondly (hope it`s ok to post two things in one here?), while inspecting the Distribution Boards we discovered that nearly all of the supply Neutrals are far smaller than the phase conductors. The occupants of the factory are not the people the building was originally designed for and there is quite a lot of equipment now requiring Neutral connections (am thinking that originally the Neutral would have been just for local lighting and small power). Would you agree that we should advise the customer to increase the size of the Neutrals to that of the Phase conductors? (In some cases the Phase conductors are 120mm with a 16mm Neutral conductor).

See section 523. If the load has increased then the neutral size should be upped to suit.

 

[Evans Electric]

Half sized neutrals was in fashion in the 1950,s early 60,s at some premises , there are SWA cables around too with a reduced neutral in them. Its not done these days but the proof is in the pudding, are there signs of overload etc , probably not in my experience.

120mm phases with a 16mm neutral .... is it a balanced load, have you read the current on the neutral ??

Secondly if you try to sneak a 2nd question in a post , The Godfather (see Forum members) will send his boys round , well you've done it now !!! But welcome to the Forum anyway.

Deke

 

[Colport]

Thanks Stuart & Deke,

The testing was done during the xmas shut down so there wasnt any real load, just the lighting was on.

Can anyone offer advice on the PFC problem please (want to get the report in pretty soon as there are several other Cat 1 faults).

 

[kme]

Col:

The PFC shouldn`t be an issue - we`ve done a hotel with a similar issue... The BS88s will deal with the PSCC for you.....

As for the reduced neutral - if either:

the major load is 3PH balanced OR

The CPD is low enough to deal with a 16mm live conductor

Then you`re fine. However, I wouldn`t be happy with any borderline reading on the neutral load.

Go in when they`re running, and stuff a clamp on the neutral (as Deke above)

HTH

KME

 

[batty]

welcome no comments on questions think its been covered.