IET logo
Decrease font size
Increase font size
Topic Title: Fuse sizing & Thermal Protection
Topic Summary:
Created On: 11 April 2013 07:51 AM
Status: Read Only
Linear : Threading : Single : Branch
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 11 April 2013 07:51 AM
User is offline View Users Profile Print this message


Posts: 6
Joined: 25 July 2008

Hi Folks,

Just found out that some bright spark (no pun intended) has fitted a 200A fuse in a 100A Red Spot holder. The equipment is a 3-phase induction motor with FLC of 90A. The previous fuse was a 100M160 and, aparently kept blowing. The cable is a 50mm armoured with max current of 151A (table 4D4A in regs).
The guy is saying that even though the 151A cable is being 'protected' by a 200A fuse it's still safe. There is a 2-phase O/L protection (as expected with motors) but i don;t think that's good enough.

Any thoughts?
 11 April 2013 09:56 AM
User is offline View Users Profile Print this message


Posts: 16394
Joined: 13 August 2003

If there's downstream overload protection, then it's just a matter of ensuring the fuses provide fault (short circuit and earth fault) protection. You'll need to do the calculations (knowing the fuse characteristics and loop impedances as well as conductor size and cable type - see regs 434.5.2/543.1.3), but it doesn't sound implausible on the face of it. (By way of example, in a domestic ring circuit a 1.5mm2 c.p.c. is usually more than adequately protected by a 30A fuse).

- Andy.

New here?

See Also:

FuseTalk Standard Edition v3.2 - © 1999-2018 FuseTalk Inc. All rights reserved.