Slow fuse vs time lag fuse

[larkim]

Need a slow fuse 2.5amp for my boiler but can only find' time delay' fuses at Maplin. Are they the same thing? Cheers! Matt

[Tabby]

IIRC slow blow have nodules on, time delay have a spring mechanism. T fuse are slower, and can replace slow fuses no problem.

NT

[Bob Eager]

A link to the DIY FAQ....

Did someone here write any of that WP stuff?

[larkim]

Have to say Wikipedia was my first stop before I went and bought any at Maplin. I "trusted" that the wiki entry which says "time delay fuse (also known as anti-surge, or slow-blow)" to convince myself that they were sufficiently close to warrant taking the risk!

Now, speaking cynically (!), I now have a service contract on the boiler, so if the PCB should blow because the fuse I have used isn't quite right, I'll simply stick back in the original blown fuse and keep schtum. Unethical, unlawful perhaps. But I suspect just what most people would do to ensure their insurance backed service contract pays up!!

Matt

[larkim]

Just for my info / sanity, can you clarify this. "Hammer" and "breaking capacity" imply physical impact. Is that the sort of situation you are imagining?

Or am I missing the point?!? (Most likely!)

Matt

[fred]

:-D

Hammer is to break the tube on your existing blown fuse to open it for examination and determine whether it is a single wire strand (with or without blob) or a spring type, and to see whether the wire remains solid with a single break (implying light overload) or vaporised (implying some high current - short circuit - fault).

Breaking capacity is the capability of the fuse to interrupt a certain level of fault current. In a high current fault, the fusewire may vaporise and 1. the vapour could conduct for a period, extending the duration of the fault current leading to further damage or 2. coat the inside of a glass envelope fuse, leaving a conducting path behind which could create a hazard.

High breaking capacity fuses generally have ceramic bodies and are sand filled to extinguish any arc that may tend to be created by the fault.

Typical breaking capacities:

20 mm glass fuse - 35A or 10x rated current value 20 mm sand-filled ceramic - 1500A BS1362 fuse, UK ring main plug - 6 kA BS1361 fuse, UK distribution board - 16 kA