Saturday, December 6, 2014

Renewable Fuses a ticking time bomb hiding in many commercail and industrial buildings when not properly applied

Renewable Fuses have been around for many years  at one time they where a very handy overload unit to have on site. If you blew a fuse you simply opened up the fuse end slid out the blown fuse link and inserted a new link or 2 links if it was a time delay fuse and away you went.

But thats where the problem started. These fuse where only meant to be used on circuits with 10,000 or less interrupting amps  like light  circuits and transformers but as usual they got misapplicated and ended up in industrial and commercial applications where there can be 50,000 or more interrupting amps  are available allowing for a very dangerous overload condition which can result in a arc flash and explosion. In the picture below on the left you see a renewable fuse which end caps can be removed and link replaced next to a modern slo-blow one time fuse made to handle 100,000 interrupting amps  but as you can see its easy to just replace one with the other.

Renewable fuse on left modern one time fuse on right

 renewable fuse apart showing replaceable link
 The other problem of course is if end caps are not properly tightened and then you had maintenance people trying to put more than 2 links in a fuse which will cause a much further than allowable time for fuse to operate. 
 When installing new equipment these renewable fuses should not be used only modern one time fuses. But it happens a fuse blows and only one available in shop is a renewable fuse and in it goes to get a machine back on line and then a problem happens.

Luckily the availability of the links is getting fewer and further apart as many manufactuers want nothing to do with them due to liability issues but they can still be found  and when i find them I remove them and replace them with proper one time fuses. 

But like anything these hazardous units where never recalled and just allowed to go away quietly 
by them selves and never issue a warning about them and most rookie electricians have never seen one let alone know there dangers. but thats NFPA and UL for you. they never ever fail to disappoint me.

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