GE Fused Disconnect Problems

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Pop wrote:

pretty hard to tell, but one thing no one mentioned is the "area" of the switch contacts. The smaller the contact area, the faster it can heat up, so if there's any hot weather relationship, it's possible the "set" you mentioned in one post was enough to actually "offset" it a tad, and thus drop the sq. in/sq. cm area of the connection. 40A running current is enough to cause some heat buildup during normal operation; so, on a hot day with a start-surge, in a super-heated attic, the buildup could take a run-away attitude. The hotter the metal gets, the more impedance it presents via its own properties, plus that faster oxidation can form, and off it goes. The heating process is often a logarithmic as opposed to linear pattern, so what takes ten seconds at first, may only take 0.1 seconds in a minute, and so on, meaning the heat increases exponentially also. Is there a heat-rise spec on the plate?

current) limit of the contacts and that the 60A spec is a timed spec: eg, 60 A for x minutes or hours vs. constant current. No, I'm not talking slo-blo type of stuff. If so, then 40A would be too much for it. This would be worth taking up with the manufacturer or better yet, their eng dept if you can find an "in" to them. Some places, Square D for instance, make it easy to talk to an engineer, others won't let you in a million years, but it's worth asking for someone with design experience, or the actual technical design specs of the switch.

design vs. use issue. Perhaps if you posted the specs from the switch plate, someone could make a better estimate.

if that extends the time it takes, or even stops the burning? Probably not; sounds like an awful long time between problems. Nah, guess it wouldn't work; too close to the fuses themselves to separate the air flow.

All good stuff thanks!
The only offsetting thing I can say is that the auxillary heaters typically only get switched on when it gets too cold outside for the heat pump to take care of the heating requirements, and that's the time of year when the attic is cold, not hot. The rest of the year the only load is just the fan motor, a pissant 2.5 amps. So, I doubt that high ambient temperature is the troublemaker.
Rather than turn this "one off" situation into a major research project, I think I'll go with replacing the GE fused disconnect with an unfused disconnect and see what happens in a year. <G>
Thanks again.
Jeff
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Jeffry Wisnia

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I'm just curious .. if you know. what make and part number fuse have you been using

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bumtracks wrote:

OK, I got your question in time to pull the remains of the fuses out of the workshop trash can.
The fuse which opened this time, because the solder holding the fuse link to the end cap next to the switch contacts melted, has GE's name on it and is marked 60 AMP, One-Time Fuse, 250 VAC or less, 10,000 Amps Internal Rating, Class H.
The other fuse in the disconnect, which fell apart when I pulled it out because the fibre had toasted but the fuse link was still intact and soldered to both caps, Was marked "Ace Hardware", Type NON, One-Time Fuse, 250 Volts or less, 50,000 Amps internal rating, Class K5.
Gee, maybe now that Matt guy will come back in to tell me the problems I've had with this disconnect were likely caused either by using an Ace Hardware fuse in a GE fused disconnect or the fact that the pair of fuses was "unbalanced" by 40,000 Amps. <G>
I am always suprised to see just how skinny fuse links actually are in relation to the gage of the wires in the circuit they are protecting. I just miked the link from one of those charred fuses and its only .008" thick by .065" wide at the narrow spots. Obviously it has to be that size to perform its function, but that small a cross section sure doesn't "look" like it'd carry 60 amps continuously.
Sorry to waste so much bandwidth on this thread guys, it's my curious mind always wanting to find the "real reason" why things happen.
Jeff

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in commercial disconnects of time gone past, it wasn't odd to see 'fuse clip clamps' adding pressure to the clip the fuse snaps into as they would get weak with age and heat up, usually just melting the link. clip clamps look like little springy packman jaws with a knob that tightens them adding additional spring pressure. imagine there's still some out there doing their job.

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bumtracks wrote:

Yep, I remember those.
But, I'm darn cerain I've got this one diagnosed corectly, as the other ends of the moving switch arms, the ones which mate with the contacts at the input terminals, also oxidize and show heat discoloration. And before somebody asks me again, the input wire terminal screws ARE tight, the wires in them are copper, not aluminum, and there's no signs of heating up there.
Also, the output ends of the fuses have never had any problems like that, the clips on those ends are still in their original (tin plated?) condition, with no signs of overheating there.
I also remember cartridge fuses with replaceable links, even in smaller sizes like 20 amps. I don't know if they are still made now that we've become used to living in a "throw away" economy.
Being a depression era baby, I really miss frugal stuff like that.
Jeff

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This is Turtle.
Yes the fuse link type fuses are still made but nobody buys them anymore. The links cost $.80 and the replacement fuse cost $1.09. It's not really worth it.
Yes we are in the Throw away Economy Generation !
TURTLE
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This is Turtle
Jeff , These fuse disconnects are stated as rated at 60 amps but if you read the amp draw rating in the data plate with it. You will see it is suppose to be used on amp draws of less than 40 amps.
It states that it will handle short time useage of near 60 amps but when put in a contenous amp draw the 40 amps your drawing on it become the max it will handle. I have the Connecuit Electric type I use on condenser outside and they are rated at 60 amps but if you read closely you will see it says contenous use 40 amps is the MAX. it will handle. You just don't run anything at Max. By running this disconnect at 40 amps is like it says on the Lexus LS-400 Maxium operating speed is 161 M.P.H. and then you can run it at that speed and be safe. So if you don't run your car at Max. Speed 160 M.P.H , Don't run your 60 Amp disconnect Rated at Max. Amps 40 Amps.
I have a rule I use and that is I will rate the load at 1/2 the rated load on the disconnect like it rated at 60 amps on the cover. I will not put more that 30 amps on it contenously.
And yes my Lexus LS-400 will go over 161 M.P.H. at 165 M.P.H. and is the model before the Kill switches put on them. And yes I drive the speed limit most of the time and also drive my disconnects below the amp limit.
TURTLE
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TURTLE wrote:

Well now, I'll check the specs and if that's the case it sure makes sense now! And too bad the original installer didn't see it that way too, it would have saved me a lot of nuisance fixups.
Thanks, and I hope the 60 amp Aquare-D non-fused plug type disconnect switch I just bough yesterday isnn's similarly rated. <G>
Jeff

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This is Turtle.
No that Square - D breaker looking disconnect is rated above the 40 amps but usely in about 2 to 4 years the breaker will burn inside the breaker and go out and then you can replace it with a real breaker square- D and keep going. A lot of HVAC people don't like them for that call back coming in 2 to 4 years. Now if you replace it now with a real breaker to apply to the application you will not see it down the road.
TURTLE
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TURTLE wrote:

Do they make a 100A disconnect that just has a pull-out block with 2 cartridge fuses in it? That's what I think I would use if they are available that big. Put in whatever size fuses you actually need to protect the heater, (45A?) or just put 100A fuses in it and let the breaker back in the main panel provide the protection.
Bob
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This is Turtle.
Yes they do but your looking at about $68.00 + Tax . It will come with a lever on the out side and spaded type fuses and the fuses are about $8.00 each even being 60 amps to 100 amps sizes. The 60 amp disconnect is the breaking point between commercial and residentiual equipment and the price reflects it. Now this type fuse box / fused type disconnect will run at 90 amps till the cows come home but the 60 amp cheap o will run till the sun goes down. .
The standard 60 amp fuse / disconnect $15.00 verses the 100 amp fuse box / fused disconnect at $78.44 is a far cry between them in quality and in price. At about 5 times the cost the public will not go for 5 times the price when Home Depot sells them for $15.00 and the home owner can replace them pretty easy.
TURTLE
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TURTLE wrote:

No, the one I bought is the "pull-out" kind. I looked at the one with the "breaker looking" switch in it and decided not to take the risk of its switch contacts fouling up by themselves. The plug-in contacts look pretty robust and feel tighter than a virgin's cooze. I'll swap it in and report back in a year or two. <G>
I'm still scratching my head in amazement that a closed switch with what appears to be adequate ratings located in a benign environment will slowly develop increased contact resistance, but I've seen it and believe it, so it must be so.
Again, my apologies for wasting all the bandwith on this simple little problem. It's my engineer's mind dammit, I have an overwhelming desire to learn why things like that happen, I guess it's one of my my retirement hobbies, thoroughly non-cost effective, but fun, like many other hobbies.
Jeff

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