Burned fuse block!!!

[mkoban]

Heres what I know.

480V/3ph/60Hz delta power system

The 480V loads in this sytem are as follows: 2 - small (<3HP) motors, 2 - 20KW immersion heaters.

This control panel has 70A Bussmann class J fuses in its main disconnect, 30A littelfuse ccmr-30 fuses in its branch circuit before the heater contactors.

I'm sent a picture of a control panel with the one heater fuse block completely charred, damaging wires throughout the panel. L2 fuse was history (exploded), L1 and L3 fuses damaged. The other heater fuse block blew L2 as well but had no charring. Two phases in the main disconnect (70A), L2 and L3, were open.

The service technician onsite indicated that the fuses in the second heater block were hot to the touch as well.

What could have caused this to happen? All the wiring downstream from the charred fuseblock appears to have its insulation. Why would these fuses not have just opened? And why would the main disconnect fuses upstream open?

I will get you more info as soon as I can get it. Any light you can shed on this would be greatly appreciated.

Thanks in advance. :shock: I've had this expression on my face all day.

 

[tshea]

Are you looking for an explanation?

Loose connection?

 

[mkoban]

So if there was a loose connection in the heater 1 circuit it could cause the charring and the fuses that blew all around the system?

Thanks for the quick reply

 

[charlie b]

Two questions:

First, is this a new installation (or one that recently underwent major maintenance), and was it being turned on for the first time? Or was this in operation for along time, and did it experience a sudden failure?

Secondly, were the heaters themselves tested for possible damage?

 

[tshea]

A loose connection anywhere in the circuit, mainly at the fuse block, could cause the fuse block to char when the fuse let loose.

Is this some type of parts washer?

If the heater shorted, you could also experience this problem.

Another place to check is the fuse holder. Was it holding the fuse tight??

If anything is loose--heat.

 

[mkoban]

This was a new installation and had only been running a few days.

The first thing that our customer did when they received this panel was to remove the Class J fuses that we had installed and put type CC fuses (littelfuse) that they stocked in their place. I am not sure if everything was tight.

I am still unclear on why this would trip out the main disconnect fuses.

The heaters are actually used to concentrate a desiccant by removing water.

Thanks,