63A 60898 ******!

[froria]

Hi guys got a little Ba****d for you.

Ive had a call to a property because the mcb which is a 63a typec 60898

This is in line just after the cutout fuse which is a BS88 type2 100amp. I'm not too sure why they opted to put the 63a in there. The submain is a 25mm 3 core swa.

The customer told me it was the kitchen ring main that was the issue. So I tested the ring main (end to ends, r1+r2, IR, Loop, ect...) all good.

So I figured hmmmm maybe a faulty appliance which should cause the 32a type b to go. So faulty 32a mcb so I replaced it. Got a call the 63amp type c has gone again. Now when I replaced tyhe 32 I also replaced the 63 for good measure.

Can someone please explain to me how the hell this is happening? There is no other switch gear in the enclosure so there is no thermal effect on the mcb. Im stumped.

Unless its another cicuit with the faulty mcb.

cheers

 

[Andy™]

overall load could be enough to trip 63a if there is a fault, but not enough on any individual circuit to trip

 

[froria]

overall load could be enough to trip 63a if there is a fault, but not enough on any individual circuit to trip

Very good point Andy mate. Thats why I ask I seem to overlook the most simple things when looking too long!

 

[SLIPSHOD & SLAPDASH]

I would swap out the MCB for a fuse.

Depending on the length of run, Zs etc you could probably fit a 80A.

 

[Evans Electric]

What load is the place pulling ?

More than 63A  I wonder?    Did you try your ammeter on the tails ?

None of the smaller MCBs are tripping so its possibly the overall current ...when showers and cookers and heaters are all on .

Sounds like the 63A is to protect the SWA  but 25mm is good for 100A  is thats the problem .

 

[wozz]

Could it be you havnt got full discrimination between the 63 and the 32 when you have a short circuit condition?

I could have read this wrong its been a long day.

 

[Steve3948]

Could be damaged SWA or loose connection.

 

[Sidewinder]

What make are the breakers.

Are they both B curve?

What loads are off the 63 that are not off the 32, and what are the base loading of these loads?

 

[froria]

What load is the place pulling ?

More than 63A  I wonder?    Did you try your ammeter on the tails ?

None of the smaller MCBs are tripping so its possibly the overall current ...when showers and cookers and heaters are all on .

Sounds like the 63A is to protect the SWA  but 25mm is good for 100A  is thats the problem .

To be honest Ive not looked into this at length yet. First thing Ill be doing when I get over there is amp clamp meter. Im sure its overload which is odd as this has been the same setup for over 5 years as with the rest of the flats. But Ill look into and let you all know.  

What make are the breakers.

Are they both B curve?

What loads are off the 63 that are not off the 32, and what are the base loading of these loads?

Both Breakers are Hegar.

32 type b  63type c

The entire flat is off the 63 only the kitchen off the 32.

 

[Sidewinder]

The whole kitchen, or just the so?

Can you please describe the install in a little more detail please?

 

[Evans Electric]

I'm thinking overload here !   Any Off Peak heating . ?

 

[Steve3948]

I'm thinking overload here ! Any Off Peak heating . ?

63A C Type though, that's some constant load for a flat.Hmmmmm maybe not a flat, my error.

 

[batty]

I never like putting in MCB's on main sub-mains much rather have a cartridge fuse any day.

 

[Evans Electric]

Type C is it  ?  Bit OTT there. 

Yes Batts I'm still a big fan of HRC fuses  for certain uses TBH .

I remember a one colour print engine we had previously connected to a 20A  TPN  HRC sw/fuse with 2.5s and moved it to new premises and a new MCB board.

Being Japanese it had a 440V to 110V  TP tranny in  line and had never been a problem  with inrush current.    As you'd expect , no way would it power up through a type B so I'd fitted a type C ...no good .. had to be type D .    

20A  NIT fuses had handled it for years but as you know MCBs are very picky .

 

[froria]

Thanks everyone for your input. On my revisit Ill get some details. I only did a fly by visit to see if it was something silly.