Remote Fused Disconnect 'Melt Down'

[Mrwurm]

Remote Fused Disconnect \'Melt Down\'

Ok, so you're probably wondering what this thread is about

Here's the biz:

I have a 'Hot tub' or 'Spa' at my home. The electrical hookup goes like this:

50 amp 220 volt breaker in the main house panel is connected to about

100 feet of #8 wire (or maybe #6) that snakes it's way to the remote fused

disconnect. The disconnect is rated for 60 amps max and a 45 amp time-delay

fuse is installed on each leg. Wiring then leaves the disconnect and travels

about six feet to the final connection at the 'hot tub.'

Now, why have I said all this

It appears that the 20 year old pump has finally siezed up and died. But, the

old pump was not satisfied to go quietly, it was determined to take other casualties

along with it.

Close investigation has uncovered the following information:

1) The 50 amp breaker at the main panel did not trip.

2) One of the 45 amp time-delay fuses died.

3) And finally, all of the plastic components in the remote disconnect have melted down
to a distorted mess. Actually, only the side with the blown fuse melted.

So, I've said all this to pose one question . . .

What good is a fuse if takes so long to blow that it allows an $80 disconnect box to
melt down and become useless ?

 

[johnday]

Re: Remote Fused Disconnect \'Melt Down\'

Mrwurm; Was it the line or load side of the fuse that fried? /forums/images/graemlins/confused.gif

 

[slowrev]

Re: Remote Fused Disconnect \'Melt Down\'

Probably the result of corrosion on the blades in the disconnect. Caused resistance and current thru the resistance caused heat. The fuses will fail from heat as well as overcurrent.

You might want to change the breaker as well though just to be safe.

Ben

 

[Steve_Miller]

Re: Remote Fused Disconnect \'Melt Down\'

What was the full load current of the motor?

Steve

 

[Highbeam]

Re: Remote Fused Disconnect \'Melt Down\'

220- so each leg is working and moving the same current.

The value in that blown fuse is that it didn't start the rest of the mess on fire. The slo-blo type fuse allows for high start up current in excess of the steady maximum fused current. When that motor starts up it grabs a big chunk of current that would blow a fast acting fuse.

Go buy a new updated disconnect panel with the GFCI. Twenty years ago things may not have been as good.

The current electrical code in place when I installed my hot tub did not require the remote disconnect, I actually read it to be sure. Instead I have a GFCI 50 amp fuse at the main panel. Maybe you can skip the whole thing and hardwire it.

Get the tub working again. Nothing like whiskey in the tub.

 

[PineRidge]

Re: Remote Fused Disconnect \'Melt Down\'

In my years in the HVAC business I would see all kinds of electrical damage done by air conditioners with plugged air cooled condensers. The amp draw would inflate slowly over a period of time and melt contactors, plastic components in outside disconnects and finally if left for an extended period of time the compressor itself. Seems the fuse or breaker was always last to go. /forums/images/graemlins/frown.gif

Most likely taking an amp reading, with a clamp on ampmeter of your pump motor may have even told you early on that it was doomed for disaster. Amp draws elevate with tight bearings and or restricted air flow due to dirt plugged motors.

 

[Inspector507]

Re: Remote Fused Disconnect \'Melt Down\'

Jerry,
It may have been a bad connection that caused the melt down. It could have been the terminals or the blades if any. Fuses usually will blow quicker than a breaker will trip. Time Delay will blow a little slower under load, but trip quick under short circuit.
I wonder what the total draw is?
Replace the whole mess with a 50A GFCI Spa disconnect. That is provided the spa will work on a GFCI. Some "pool pumps" manufactured before 1985 will trip a GFCI in a heartbeat. I had one that would trip in 20 seconds.

 

[_RaT_]

Re: Remote Fused Disconnect \'Melt Down\'

Jerry, you said what I would have said. As an electrician, most of the problems I encounter on "after" installations are bad connections. This is compounded with aluminum since it crushes easily and need s at least a couple of retorqueings. I suspect a poor connection did the fused disconnect in.

 

[johnday]

Re: Remote Fused Disconnect \'Melt Down\'

Mrwurm; The reason I asked which side of the fuse block fried, it could help in trouble shooting your 50amp feed. 507 should correct me if I'm wrong, but if it's on the load side it would indicate to me that the breaker in the house is probably fine. The fuse did it job, just not quick enough. Take Inspector 507's advice and replace your disconnect with a new enclosure and GFCI. Sounds like your pump motor went to ground. I think I'd also be a little concerned about the feed out of your old disconnect also. If you fried that box like you did, who knows what may have been done to the feed as well.
I'm only offering suggestions, Inspector 507 knows what he's talking about. /forums/images/graemlins/wink.gif /forums/images/graemlins/grin.gif

Where are you in SE Mich? If your close to Monroe it'd be no big deal for me to take a look. /forums/images/graemlins/grin.gif

 

[Steve_Miller]

Re: Remote Fused Disconnect \'Melt Down\'

Not necessarily, if either side found a path to ground, it will take it. I suspect the same as the rest of you that there was a bad connection that just overheated. I'm just curious what would draw 40-50 amps in a hot tub. If it is a motor then it should be protected by an overload of some type. If there were multiple devices then each should be protected individually (i.e. heaters, lights, circulators). Don't know anything about spas or hot tubs so bare with me.

Steve