I have had a machine panel burn up twice without blowing a fuse at the disconect or a fuse in the machine panel. Voltage is 208 3-phase and measures corectly phase to phase and phase to ground. What can cause this to happen?

 

There is just not enough information provided in your post to give you an answer.

For one thing, "burn up" does not mean anything specific. It might mean a fire started inside the panel, or a single small component failed with some black smoke, or all kinds of other things.

It would be helpful if you gave us additional information such as:

what kind of machine is the panel controlling?
what types of devices are in the panel?
exactly what kind of damage was incurred and to what devices?
how much power is going thru the panel?
who designed and built the panel? i.e. - do you know it was done by someone competent?

To directly answer your question, one answer could be that fuses do not protect against fire. they protect against electrical shorts and overloads, presuming they are sized properly to protect the load. It is possible that a circuit might not be protected by a small enough fuse and could have a short circuit or overload that is not cleared by the fuse. it is also possible that the circuit that smoked was not protected by any fuse at all.

--
Bob

 

You're going to need to be a little more specific when you say the panel burned up.

Did you have some power resistors in the panel get fried? Was some wiring reduced to ash, or lost its insulation?

How big is the panel? What type of components are in the panel and what is it controlling?

Etc. etc.

 

Evidently some kind of a thermal issue unrelated to overcurrent. Check for loose connections and other sources of heat, both electrical and otherwise.

 

A 1 amp fuse will carry 2 amps for some considerable time before blowing. Fuses are designed to carry as much as twice their rated current for several seconds. Slow blow fuses can last for even longer. This is the reason that fuses only really protect against dead shorts. Your fuse needs to be as small as possible to provide effective protection. Also, if you have components that run lower currents in your panel they may need individual fusing. And remember that the fuse doesn't blow until the high current has already occurred.

Of course all this is beside the point. Your board should not be catching fire in the first place.

 

Gary... can you provide some detail as to what "burned"? Was metal melted? How about photos?

Regards, Phil Corso (cepsicon[at]AOL[dot]com)

 

sounds like a starter cabinet, fuses are notoriously unreliable; however, it is possible that you had a phase to phase short before going through the fuses.

this is quite common possibility in dusty conditions.

but in agreement with the other responders you need a little more detail than you have presented thus far.