Quick PFC question.

[La Poste]

I have just been asked a question by a friend of mine and am not sure of the answer.

He has done a PFC test and found it to be 8.5 KA.

The main fuse is rated at 33KA but the MCB's (60898) are rated 6KA.

He has asked me if it will be compliant as the main fuse is rated higher than the PFC but I am not sure.

Can anyone help me with this one?

Thanks.

 

[Hiddo]

How did your friend test the PFC?

 

[Welchyboy]

Have a look at 434.5.1, can he not install 10ka mcbs?

 

[Des 56]

Is this a domestic installation

 

[telectrix]

if he's measured at the incoming side of the main switch, then it's the breaking capacity of the main fuse that is relevant.

 

[La Poste]

I guess he measured at the incoming side of the main switch.

I will send him a text and ask some more questions.

Would it be prudent to measure at the outgoing side of each MCB just to see what the figures are?

If the PFC is greater than 6KA at the outgoing side of the MCB then he will be in trouble right???

 

[Welchyboy]

the reading will not differ much at the mcbs, if he has some large outgoing final circuits he may a problem if a short circuit occurs near the origin of the circuit

 

[Des 56]

Is this a domestic installation

 

[La Poste]

Is this a domestic installation

Not sure, I guess so.
I will get more info.

 

[Guest123]

An extract from BS EN 60439-3.


"Part 3 of the Standard, BS EN 60439-3, deals with the particular
requirements for low voltage switchgear and control gear
assemblies intended to be installed in places where unskilled
persons have access to their use. This covers the supplementary
requirements for enclosure distribution boards suitable for indoor
use containing protective devices intended for use either in
domestic applications or other locations where unskilled persons
have access. Control and/or signalling devices may also be
included.
These distribution assemblies are for use on AC supplies, with a
nominal voltage to earth not exceeding 300V. The outgoing
circuits include short circuit protective devices, each having a
rated current not exceeding 125A with a total incoming load
current not exceeding 250A.
In the UK, such equipment is referred to as a ‘Consumer Unit’
and as such is covered by this Standard. However, additional
requirements from annex ZA of the standard call for the
assembly to have an additional test; this is known as the
‘conditional withstand test’. The condition is that the consumer
unit must withstand a 16kA short circuit fault when protected by
a 100A HRC fuse to BS 1361 type II. Further requirements are
addressed by this annex:
• Means of isolation to be via a manual double pole switch
disconnector
• Rated current of consumer unit is determined by current
rating of incoming device.
• Outgoing protective devices can be MCB’s, Fuses and/or
RCBO’s."

 

[La Poste]

So the boards and also the MCB's are tested to 16KA right?

The problem seems also that if there is a short circuit line to neutral fault the MCB might be damaged and need replacing.

Testing these boards to 16KA, are they still usable afterwards or do the MCB's need replacing?

A lot of questions but thanks for the help.

 

[MarkieSparkie]

This product test is destructive in nature. The manufacturer's test at 16kA exceeds the MCBs Icn "one-time" fault current rating, often resulting in major damage to the DB, cabling and occasionally MCBs explode. However, the fault current must be interrupted in any unit that passes the test and therefore meets the standard.

 

[Chr!s]

So the boards and also the MCB's are tested to 16KA right?

If its a consumer unit along with protective devices complying to BSEN 60439-3 and the manufactures are utilizing the conditional short circuit test in Annex ZA of that standard then yes.

The problem seems also that if there is a short circuit line to neutral fault the MCB might be damaged and need replacing.

Possibly, it all depends on what the level of fault, PFC can be greatly reduced along the out going circuits.

Testing these boards to 16KA, are they still usable afterwards or do the MCB's need replacing?

If an MCB rated at 6kA is exposed to a current of 16kA Then it will need to be replaced, bear in mind at 16kA the 100amp Fuse will limit the current to around 9kA, even so the mcb would require replacement.

A lot of questions but thanks for the help.

Regards
Chris