MCB tripping Amptec C1200

Hi All,

hoping you can help? Just moved into a new house with a Heatrae Amptec C1200 heating system. The MCB is tripping roughly twice daily - usually when system has been off for a while and starting a new programme. 
 

background info:

Electric boiler is on DB2 (no other circuits on DB2)

Boiler is on BG 50A MCB  

Boiler rating is 12KW 

cable running from DB2 to Amptec is Drakaflex H07RN-F 450/750v 3G 10mm2 - cable length approx 1.5m 

ambient temperate in cupboard due to boiler running is circa 35-40 degrees. 
 

my initial thoughts:

1. Replace the MCB with a 63A as 12000/230 = 52A. Could drawing 52A be causing the MCB to overheat? 
 

2. Cable 10mm2 probably ok even with correction factor applied for ambient temp for 90 degree thermoplastic? 
 

had the installer boiler company out and they said to bleed the radiators and turned down the output temp of the boiler. Still continuing to trip the MCB. 

apologies if I’ve posted this is the wrong place. Really appreciate your views on this 

regards,
 

Al 
 

In the DB is the B50 next to other MCB's?

If it is and if there is space move it so it has a blank space each side of it. 

Have you cot a clamp current meter to actually measure the current it is drawing?  The 12kW could well be at 240V so actual current drawn could be more or less depending on what your actual mains voltage is. 

If measured current is <50A replace the MCB as a first step.

With temperature correction for that type of cable you'd be looking at 16mm even on a 50 amp MCB.

As the circuit is right on the rating of the MCB it's probably become 'tired' over time and will need replacing.

Double check with the manufacturers but I would look at swapping for 63 amp MCB and 16mm cable. Table 4F1A of the BBB and column 3 of table 4B1 40C.

AP84 said:

Cable 10mm2 probably ok even with correction factor applied for ambient temp for 90 degree thermoplastic?

Click to expand...

Are terminals rated for 90°?

Thank you all. Have the manufacturers service dept coming to have a look on Monday. It’s still under warranty so not going to touch it until they’ve seen it. 

Pro Dave - on a DB board on its own and has blank spaces each side. 
 

Sidney - thanks for the table references will have a look at this 

Kerching - didn’t think of this - will look into it further 

will let you guys know what the service engineer says. 
 

Have a good evening 

Al 

you cannot  use the full 90° thermosetting rating unless ALL associated terminals are rated at that temperature