ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

ECN Shout Chat
Top Posters(30 Days)
Admin 19
Recent Posts
Anyone hiring inspectors?
by HotLine1. 03/27/17 08:03 AM
Old decora style outlets
by Admin. 03/25/17 11:40 AM
ESA Arc flash course
by TheShockDoctors. 03/24/17 10:15 AM
fuse rejectors
by HotLine1. 03/24/17 07:53 AM
Another Forum Update
by Admin. 03/22/17 03:04 PM
New in the Gallery:
SE cable question
Popular Topics(Views)
231,640 Are you busy
166,517 Re: Forum
160,724 Need opinion
Who's Online Now
1 registered members (Tjia1981), 70 guests, and 8 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#29795 - 09/25/03 09:38 AM Blown fuses  
Joe Carpenter  Offline
Member
Joined: Dec 2001
Posts: 50
USA
We have a halogen oven in our plant that is powered by 480volts. It is a pretty basic setup. The line feeding it is protected by a 125 amp breaker. All the legs going to the halogen lights are protected by fuses. There are 5 small circulating fans on this oven and each leg of each of the fans is fuse protected (15 fuses).
My problem is this:
Last night during normal operation the 3 3amp fuses on circulating fan #4 failed. They literally exploded and burned up. It tripped the 125 amp breaker feeding the oven. No other fuses or OL's were blown or tripped.

This morning I and another LE were investigating and we simply could not find the cause. No short circuits, nothing. We replaced the fuse blocks and the fuses and turned it back on and everything is running normal.
I am still puzzeled over why this happened. The fuses were Bussman Low peak LP-CC 3a 600v class CC time delay fuses with an A.I.R. of 20k.

I replaced them with fuses with Ferraz Shawmut "amp-trap" ATDR fuses with a rating of 200k.
I figured the rating was not high enough on the original fuses or they would not have exploded.

I know I did not go into a lot of detail here but Does anyone have any ideas what could have been the real problem ?

Also would it be unreasonable to expect the oven manufacturer to have put in fuses with a 200k rating rather then the 20 k.?


Work Gear for Electricians and the Trades

#29796 - 09/25/03 10:38 AM Re: Blown fuses  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
The LP-CC fuse has a 200k rating, not 20k. Are you sure that they exploded and didn't just burn up? A poor connection at the fuse clip or wire termination point will often cause the fuse to burn up.
don


Don(resqcapt19)

#29797 - 09/25/03 11:07 AM Re: Blown fuses  
Joe Carpenter  Offline
Member
Joined: Dec 2001
Posts: 50
USA
I would tend to beleive there was an explosion because some of the controllers that were mounted through the front cover it blew out onto the floor. The fuses themselves are pretty much intact except for some of the metal burnt off.
You are right about the 200k. The 20k rating is for DC.
The wire termination connection was definatly less then ideal. I noticed on some of them the insulation was not stripped back far enough and some of it was under the clamp which is obviously a problem. However, that did not seem to be the culprit in this incident because there were no signs of overheating at the terminations themselves.
The only place where I saw signs of overheating were the fuse clips themselves. And when I pulled the fuses out of the clips the clip had no discoloration where it made contact with the fuse.
That to me seems like the heat was not generated due to a weak fuse clip.


#29798 - 09/25/03 02:11 PM Re: Blown fuses  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
If the load on the three fuses is reasonably balanced, a millivolt-drop test might be done on the presently-installed fuses and fuseholders

See ecmweb.com/ar/electric_testing_contact_quality/index.htm—"Testing Contact Quality on Live Motor Starters". Understand that this involves dealing with energized circuits, so may not be appropriate unless you are adequately qualified and trained in live-troubleshooting practices.

Designers are sometimes pressured to make control gear as small a possible, and in doing so may choose class-CC over class-J fuses. I don’t think that’s always the best idea.



Member Spotlight
JoeKP
JoeKP
Berkley, MA
Posts: 144
Joined: March 2008
Show All Member Profiles 
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.015s Queries: 14 (0.003s) Memory: 0.7593 MB (Peak: 0.8882 MB) Zlib enabled. Server Time: 2017-03-28 12:05:31 UTC