IET logo
 
IET
Decrease font size
Increase font size
Topic Title: BS 3036 time/current characteristics function
Topic Summary:
Created On: 05 September 2013 11:01 PM
Status: Post and Reply
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.
 05 September 2013 11:01 PM
User is offline View Users Profile Print this message



Talex

Posts: 6
Joined: 05 September 2013

I'm trying to find a function for the current/time characteristics of the various sizes of BS 3036 semi-enclosed fuses.

It is difficult to read off coordinate pairs from the logarithmic graph provided in BS 7671 and although I've succeeded in identifying a simple exponential model using the reciprocal of current as the explanatory variable it is only reasonably accurate over the 0.1 to 5 s time range.

Any suggestions appreciated. Thanks.
 06 September 2013 08:58 AM
User is offline View Users Profile Print this message



John Peckham

Posts: 7258
Joined: 23 April 2005

Talex

Welcome to the forum.

If you have access to Amtech Protect you can plot the curve for a given fuse and use the cross hairs to read off the current and disconnection time. If you don't have this software PM me and I don't mind reading off a few values for you?

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 07 September 2013 01:35 AM
User is offline View Users Profile Print this message



Talex

Posts: 6
Joined: 05 September 2013

Many thanks for the prompt and helpful offer John.

These characteristic curves look like piece-wise functions each comprising about 8 to 10 subfunctions. I can't think of a simple single function over the full domain of any given fuse size. I could carry on in like manner as mentioned above for several subdomains to produce a usable piece-wise function but it is excessive for my original goal which is to identify the prospective current associated to 3 600 seconds for each of the 7 fuse sizes. I should therefore be grateful if you could look up those 7 values.

Secondly, having had a rough glance at the two graphs in BS 7671, I am a bit surprised to see that both the 45A and 60A (rated) curves asymptotically approach 100 A prospective current. Do both of these fuses really approach this limiting value? I'd have expected the 45A rated fuse to approach a lower limiting prospective current.

Thanks again.
 07 September 2013 06:24 AM
User is offline View Users Profile Print this message


Avatar for GeoffBlackwell.
GeoffBlackwell

Posts: 3432
Joined: 18 January 2003

I am not aware of any single function that can map these curves over anything other than a small section.

I did investigate this sometime ago when I was trying to produce a means of generating the curve data.

One of the commercial software packages takes 16 points on the curve and joins them with straight lines. You can, of course, improve on this by finding 'best fit' functions between each point but the amount of effort would probably not be justified for BS3036 devices.

Here are some old posts that included this topic.
">http://www.theiet.org/...s/f.....light_key=y


">http://www.theiet.org/for...highlight_key=y


Secondly, having had a rough glance at the two graphs in BS 7671, I am a bit surprised to see that both the 45A and 60A (rated) curves asymptotically approach 100 A prospective current. Do both of these fuses really approach this limiting value? I'd have expected the 45A rated fuse to approach a lower limiting prospective current.


I don't know the source of these particular graphs as BS3036 does not give them - it just indicates that they should be produced by the manufacturer.

Bear in mind that the minimum fusing current tests for both of these fuses is 1.5 hours.

Attempting to extend the graphs beyond 10000 seconds is unlikely to produce accurate results.

Regards

Geoff Blackwell
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.