softening the startup load on my table saw?

I have a Sheppach table saw which constantly blows the fuse on startup. On
the motor it says 14.5 amps at 230 volts, which I interpret to be about 4 1
/2 horsepower. I share my power with a bathroom fixtures supplier, and they
have the keys to the fuse box. Daytimes it's no problem. They are friendly
enough about switching my power back on. But, if they aren't there and the
power goes off, then I'm stuck for the day. People have suggested UPS's, b
ut I don't see any fit for my application. Any way to simply limit the curr
ent spike for this motor on startup?
Reply to
robobass
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The first thing you might try is changing the breaker. As they get old they tend to trip at lower current and repeated trippings will accelerate the aging process.
-jim
Reply to
jim
Fuse or circuit breaker?
I've seen this problem in a workshop I frequent in the UK where a diamond saw would frequently trip the breaker on start-up even though the motor run current was well below the breaker rating. IIRC a 1.5hp motor and a 16A single phase supply, the saw motor having additional inertia loads of the saw blade via a small belt reduction. The breaker turned out to be unsuitable for motor starting loads, IIRC it was a B class breaker and when swapped to a C class the problem went away. Still a 16A breaker but its trip characteristics were tailored to motor start loads or similar. I had discussed this with a couple of electricians and both agreed that was the issue but it just seems difficult to get them in as they all seem busy, the second one did get the chance to change the breaker and all then sorted and certified.
Reply to
David Billington
If you can get a motor-rated breaker, that would be a big help. Otherwise, get a 3-phase motor, if possible, and a VFD. The VFD can be programmed for and rate of starting ramp-up you desire. This will prevent it from drawing a big surge at start-up.
Jon
Reply to
Jon Elson
Possibles:
1- Replace regular fuse with same-amp slo-blow fuse type. 2- Replace regular fuse with same-amp circuit breaker. 3- Install a slightly larger fuse in the circuit. 4- Call Sheppach and ask them for advice.
#3 is not code-approved, but it's not really dangerous. I've seen people replace 15A fuses with 20-ampers and never get into trouble, but a possibility is there (for -sustained- higher-than-normal load) And the bathroom fixtures supplier shouldn't have any problem at all with #1 or 2.
Reply to
Larry Jaques
A 50 foot extention cord would likely do it - particularly if it is a bit light - - - -
What is the circuit fused at?? Would a time delay fuse (aka fusetron) solve the startup current problem??
Reply to
clare
The OP DID say "blows the fuse", so if that is true, there is no brewaker to deteriorate.
Reply to
clare
If it is 4HP there is a very STRONG chance it can be re-jumpered for 240 volts. I had the same problem with my compressor - 240 fixed it.
Reply to
clare
I have a Sheppach table saw which constantly blows the fuse on startup. On the motor it says 14.5 amps at 230 volts, which I interpret to be about 4 1/2 horsepower. I share my power with a bathroom fixtures supplier, and they have the keys to the fuse box. Daytimes it's no problem. They are friendly enough about switching my power back on. But, if they aren't there and the power goes off, then I'm stuck for the day. People have suggested UPS's, but I don't see any fit for my application. Any way to simply limit the current spike for this motor on startup?
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jsw
Reply to
Jim Wilkins
I'm guessing there is a breaker since he said they don't mind switching it back on.
Reply to
jim
You've gotten suggestions to get a motor rated breaker, which would be the proper choice.
However -- at 4-1/2 HP, you are in the size range where a three-phase motor is a good fit. If that motor *is* three phase, then consider getting a VFD to go between it and the wall. A VFD can be configured to take however long you like to spin up to full speed, and in the process to reduce the starting current significantly. (Even if you have no benefit from the variable speed part of it all. :-)
Enjoy, DoN.
Reply to
DoN. Nichols
[ ... ]
He is *already* running at 230 VAC which is just another way of saying 240 VAC these days. Normal outlet voltage has been changing over the years. I remember some equipment rated at 110 V, then 115 V, then 117 V, and now 120 V. 230/240 is simply double whichever voltage is the current one.
And 14.5 A is pretty high for an outlet-connected motor, and would be certain to pop a 15A breaker. If the wiring is heavy-duty, he may have 20A braker and outlets. But a motor rated breaker, with the curve which allows longer/higher start-up currents while working at the normal current for really long-term power drains..
Enjoy, DoN.
Reply to
DoN. Nichols
Does he mean "change the motor jumpers from 230 to 240" if it has taps to do that?
Reply to
John G
Thanks everyone for all the advice. To clarify, it's a 16 amp breaker, 230v . I haven't looked at it, but it's almost certainly not a special "motor ra ted breaker". I'll try that first, as that would be quick and cheap. I didn 't realize until last night how big that motor was. In principal I have 3.8 kw on the circuit, which I have been abusing, running about 3kw for heating and not always shutting that down before starting up the saw. The box is c lose by, and it would be easy enough to run another circuit or two to the s hop, but the toilet guys are typical cautious Germans and won't let me do i t myself. Paying an electrician to do it would naturally be expensive, but I suppose I'll have to bite the bullet at some point. For now I just have t o be diligent about managing my current draw.
Reply to
robobass
Except that from the OPs other postings he is based in Germany and this will be running off a single phase 230V supply not a US type centre tapped style supply so the 110V to 120V changes have no bearing.
Reply to
David Billington
Ask if you could do the work yourself and then let the electrician connect it all up for you. That'll save you a lot of money. Find an electrician who'll do it for you, then check with the store owners.
You shouldn't have a saw and heater on the same line, anyway. It's no wonder you're blowing breakers.
Reply to
Larry Jaques
Correct. AFAIK, we don't even do three phase here, just single phase 230 and 400. 40 0 is preferred for stoves and electric water and room heaters, which are co mmon here since gas is more expensive than in US, but most older buildings don't have it. In my apartment building, we do central heat and hot water w ith a gas boiler in the cellar, but no gas to the units. Also interesting, most industrial machinery runs only on 400v, and the motors are rarely conv ertible. There is a lot of nonscientific thought here. I was warned to avoi d a 230v lathe, even though it was only 750w. I was like..."your microwave oven (also distrusted here) sucks more power than that! What's wrong with r unning a lathe with 230v?"
Reply to
robobass
Yes, that's the plan. It will still be expensive though. These guys here are insane, and people put up with it.
Agreed. No choice at the moment. Only one line.
Reply to
robobass

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