Machine tool fuse question

Sounds like circuit breakers may be worth considering.

Contact my college buddy Mike Wright at Stabilant

He produces a magic clear conductivity improving liquid called "Stabilant" which worked great for me. I used to suffer 40 and 60 amp cartridge fuses blowing in the fused disconnects (four of them) supplying the two heat pump systems in our home, and I was using those "lag" fuses too.

I traced it down to contact resistance heating of the switch contacts themselves being conducted to the fuse clips and overheating the links inside the fuses.

Since I cleaned the switch contacts real good and applied Stabilant to them and the fuse clips too, I haven't had any more problems.

Tell Mike I sent you...He's near Toronto in Canada, but he ships all over the world.

Good Luck,

Jeff

Leave the disconnects, replace the fuses with copper bars, and _add_ breakers just upstream of the disconnects.

Just an idea, Bob

I am no pro at fuses but I use slow-blow fuses and I've never ever popped one in the last 7 years.

Grant Erw> For a lot of my 3ph 220v machines I use 30 amp renewable fuses. Well, often

I'm starting to see the light and will pick-up a couple boxes of 1-shot time delay. Thanks!

"Tom Gardner" wrote in news:Ga7%b.5695$ snipped-for-privacy@newssvr28.news.prodigy.com:

You should be using time-delay fuses for motor loads. The starting current of a motor is MUCH more than the running load. We have over 1000 machines, and popping a bus fuse is an extremely rare event (dead short in a motor or something as bad). Also, if the equipment uses a running load of say 20A, you want your fuses rated at 125% of that.

Proper short circuit and over-current protection are two different things especially in a motor branch circuit. If you are blowing fuses at the rate you are claiming there is something wrong. First off motors should have the protection of a thermal overload. These closely monitor the current the motor is drawing and if the motor pulls to much current the thermal elements heat up and trip out the motor control circuit. Technically your fuses main job is short circuit protection and slow blow fuses take into account the high inrush of a motor starting load. Fuses today are designed to stop huge fault currents and renewable fuses just aren't capable of that protection. I don't know where you are located but last I knew replaceable fuse elements had been outlawed. I have been in the electrical industry for 20 years and have never seen any for sale or anyone try to buy them. tim

Hey Tom,

EXACTLY what sizes are you interested in. Both ampacity and physical size. I have a pretty good cart load of one-time fuses. No renewable link though, as they are illegal here. Got a bunch of adapters to allow placing a smaller fuse in a larger disconnect, which would happen in the case of 220 volt fuses in a 600 volt disconnect.

Have you any indication as to WHY you blow so many fuses?

Take care.

Brian Laws>I'm starting to see the light and will pick-up a couple boxes of 1-shot time

The branch circuits are sized to 125% FLA of the largest motor load, the sum of the FLA of other motors plus the ampacity or any other loads. The FLA for motors are found in table 430.6(A)(1) (430.24) A 3 phase squirrel cage can have it's branch circuit fuses rated at 300% for non time delays and 175% for a time delay fuse. (430.52)

Nate

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Well, in the case of the hydraulic pump today, I suggested to the opperator to unpack the sawdust from the pump motor. It drives a BIG drill press that drills 60 holes at a time in hardwood blocks and makes a lot of drilling chips and the opperator is suposed to clear the chips every hour or so. Most other fuses blow to machine jams and the fuses pop before the mag starter heaters drop. A lot of the fused disconnects have poor contact with the fuses. A lot of this stuff is OLD and it's hard to stay on top of PM. Any new ( Hey Tom,

Why on EARTH are you blowing this many fuses? There has to be something REALLY wrong here! Oh, you are using fast-blow fuses on motors - that is probably a major part of the problem. They tend to get thermal fatigue due to the momentary overcurrent on every start. Yes, of course, get motor-rated fuses for all the ones that you have this problem with. Proper category fuses should last 15 or more years without a nuisance blow. Fuses still will get thermal fatigue, but it should be a very rare occurrance!

There are some things that are used for this. There is a silver-bearing powder and a silver-bearing "goo", I'm not sure which is best for the fuse clips. Talk to somebody at a commercial electrical parts supplier - they've been through all this many times.

Jon

On a side note, I found a place that carries those little 5x20mm fuses, fast and slow blow.

. They happen to be local to me, but I found them on the web first. These fuses are in tons of other electronic devices, and radio shack doesn't seem to carry them.

They are terrible @240VAC, especially in an industrial situation with a lot of fault current. They can literally explode. I tested quite a few of them because our Japanese supplier insisted on using them instead of the good old 1.25" types. Replace them with the ceramic type if you have such a situation. Only disadvantage is you can't see when they are blown.

Best regards, Spehro Pefhany

An excellent example of inch being better than metric :)