Fuse blowing

[strippers&dykes]

200 amp jjn fuse keeps blowing and melting main fuse pullout. Problem only occurs when a/c is ran. Recently replaced the fuse pullout and is doing it again. Equipment is square d and is pretty old and beat down. A/C is a 60 amp and fuses are fine in disconnect. When I replaced the fuse pullout I went through and tightened everything. Checked voltages and loads and everything was fine, a/c was at 28amps on #6. This evening it melted the fuse pullout and blew out the B phase fuse. Any suggestions?

 

[zog]

200 amp jjn fuse keeps blowing and melting main fuse pullout. Problem only occurs when a/c is ran. Recently replaced the fuse pullout and is doing it again. Equipment is square d and is pretty old and beat down. A/C is a 60 amp and fuses are fine in disconnect. When I replaced the fuse pullout I went through and tightened everything. Checked voltages and loads and everything was fine, a/c was at 28amps on #6. This evening it melted the fuse pullout and blew out the B phase fuse. Any suggestions?

Um, Megger the AC unit.

 

[ptonsparky]

Did you replace the complete main? Just replacing the pullout can be a waste of time. Get a good meter out and do a FOP, or scan it with a small thermal handheld. They are a good reasonably priced item for your tool bag.

 

[strippers&dykes]

Did you replace the complete main? Just replacing the pullout can be a waste of time. Get a good meter out and do a FOP, or scan it with a small thermal handheld. They are a good reasonably priced item for your tool bag.

The main is a 1200 amp that feeds 8 other suites

 

[Electric-Light]

JJN is listed as a very fast acting fuse, non-time delay fuse. Is it the right type of fuse for whatever the thread starter is doing?

 

[hurk27]

The main is a 1200 amp that feeds 8 other suites

I think what post 3 was referring to, or trying to say is that with most pullout type disconnects, the stabs will heat up and start to loose continuity, the fuse clips will no longer hold the fuse tightly, and the stab the pullout plugs into have also been weaken, this heat takes the temper out of the harden copper alloy and unless both the pullout and the contact base it slides into are replaced, you will always have a reoccurring problem.

 

[ptonsparky]

I think what post 3 was referring to, or trying to say is that with most pullout type disconnects, the stabs will heat up and start to loose continuity, the fuse clips will no longer hold the fuse tightly, and the stab the pullout plugs into have also been weaken, this heat takes the temper out of the harden copper alloy and unless both the pullout and the contact base it slides into are replaced, you will always have a reoccurring problem.

Yup.

and as stated the fuse type isn't right either. The fuse isn't melting the holder, most likely the other way around.

 

[Cow]

I agree with the others. Check for the proper fuse type and look into getting the fuse clips/holder replaced. We've had this same problem with fused disconnects in the past. It seems if you run them right near full ampacity it'll shorten their lifespan quite a bit, down to just a few years, in one case.