Question for you electricians

tito

tito

Joined
May 30, 2006
Messages
670
I'm moving into my new shop, and have found out that my 1.5h, 110v, 15A belt grinder SOMETIMES trips the 20A breaker.

I have a pulley system on the motor, and the problem arises when the pulley is set for the highest belt speed - it runs fine otherwise.

Shop wiring is all 12ga - it's run from the breaker box in the garage, underground to the shop out back, and there are 4 identical circuits. The grinder trips all of them on high speed.

At my previous shop, this wasn't an issue with 12ga wiring and a 20A breaker (although the florescent light I had plugged into the same circuit would dim until the grinder got up to speed).

There's no other equipment running on the circuit with the grinder when it trips.

Can anyone tell me if there is a (safe) quick fix for this? I can run a 220V circuit and switch the motor, but it would not be fun. Is there an easier way?
 
How far is the 12g wire run to the shop? Sometimes if the run is too far you should use either 10g or 8g depending on the loads. Common mistake. Probably not the breaker just the small guage wire getting hot and raiseing the resistance to trip the breaker.

You can only run 20 amps on 12g wire if the run is less than about 25 ft if I remember correctly, then it drops to like 15 amps at around 40ft.

10 guage can carry 30 amps at about 25 ft. and 15 amps at 50ft.
8 guage can carry 40 amps at 30ft and 20 amps at 50ft.
you may want to refrence the NEC or an Ugly's hand book (most electricians have a NEC) or just look up wire size and amp draw chart on the net.
 
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at this stage You could rewire the motor to run on 220, fairly easily. Switch to a twist lock plug to ensure no one plugs a u ground plug into a 220 u ground socket.

FB
 
Definately upgrade the feed to your shop. Just putting a bigger breaker in is asking for trouble.
 
Rusty McDonald said:
How far is the 12g wire run to the shop? Sometimes if the run is too far you should use either 10g or 8g depending on the loads. Common mistake. Probably not the breaker just the small guage wire getting hot and raiseing the resistance to trip the breaker.

You can only run 20 amps on 12g wire if the run is less than about 25 ft if I remember correctly, then it drops to like 15 amps at around 40ft.

10 guage can carry 30 amps at about 25 ft. and 15 amps at 50ft.
8 guage can carry 40 amps at 30ft and 20 amps at 50ft.
you may want to refrence the NEC or an Ugly's hand book (most electricians have a NEC) or just look up wire size and amp draw chart on the net.
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jll346 said:
Definately upgrade the feed to your shop. Just putting a bigger breaker in is asking for trouble.
Click to expand...

These gents are on the money. Too long a run on too small a gauge wire. The fix is to re-run the feed using larger gauge wire. I think you would be fine if you went to 10 gauge wire with a 20 amp breaker. (10 gauge on a normal short run would be good for 30 amps.) But here is a page with a calculator that will let you calculate (scroll to the bottom):
http://www.powerstream.com/Wire_Size.htm
 
Rusty McDonald said:
How far is the 12g wire run to the shop? Sometimes if the run is too far you should use either 10g or 8g depending on the loads. Common mistake. Probably not the breaker just the small guage wire getting hot and raiseing the resistance to trip the breaker.

You can only run 20 amps on 12g wire if the run is less than about 25 ft if I remember correctly, then it drops to like 15 amps at around 40ft.

10 guage can carry 30 amps at about 25 ft. and 15 amps at 50ft.
8 guage can carry 40 amps at 30ft and 20 amps at 50ft.
you may want to refrence the NEC or an Ugly's hand book (most electricians have a NEC) or just look up wire size and amp draw chart on the net.
Click to expand...

After pulling out some sheetrock in my garage, I discovered that the circuit run is actually made with a heavier gauge wire, 8 or 10, but I'm not sure which (it's the grey sheathing). It's about a 50-60' run, though, so I'm guessing the length of the run is still the issue.

I think since I have to run a new wire, I might as well convert to 220V. Thanks for all the help and advice.
 
What I think is happening is that you're asking for too much startup torque with that pulley ratio, requiring the corresponding high current. Startup currents in my experience can greatly exceed the RMS current of a motor (or any device for that matter). What could cure this is putting in a slower fuse of the same value. You can then, for a very short time, draw higher current than the rating of the fuse to allow for heavy starting equipment. I believe there are also some electrical doodads you can put in line with the motor to slow start it, but you're on your own on that one.

CHeers ROdy
 
Rody said:
What I think is happening is that you're asking for too much startup torque with that pulley ratio, requiring the corresponding high current. Startup currents in my experience can greatly exceed the RMS current of a motor (or any device for that matter). What could cure this is putting in a slower fuse of the same value. You can then, for a very short time, draw higher current than the rating of the fuse to allow for heavy starting equipment. I believe there are also some electrical doodads you can put in line with the motor to slow start it, but you're on your own on that one.

CHeers ROdy
Click to expand...

Yes, I was wondering about that also. I didn't know there were breakers out there like that - I'll have to check in town to see if I can find one - it will be much easier than running a new wire in a crowded, underground conduit. Thanks for the information.
 
tito said:
After pulling out some sheetrock in my garage, I discovered that the circuit run is actually made with a heavier gauge wire, 8 or 10, but I'm not sure which (it's the grey sheathing). It's about a 50-60' run, though, so I'm guessing the length of the run is still the issue.

I think since I have to run a new wire, I might as well convert to 220V. Thanks for all the help and advice.
Click to expand...

I am unaware of any color code on sheathing that indicates wire guage. You will need to check the actual wire diameters. Gray or black sheathing is often found on wire rated for underground or weather-proof wire.

There are "slow-blow" breakers as Rody described. Not sure if there is one made for 20A 110V, though. Thery are usually for heavy equipment and are used on higher amperage, higher voltage lines.
If you are looking for a slow-blow, you will likely have to go to an electrical supply house to get them.

If the breaker is tripping when you first start, the slow-blow could be a solution. But, if the breaker trips after the motor has been running for a while, changing to a slow-blow won't help because the start-up amperage pull is not the issue.
 
Usualy the under-ground or direct burrial romex that I have used many times has a grey outter insulator, heavier than regular romex. Probably 10g.

Slow blow breakers or breakers with higher "Heater" ratings realy isnt a good Idea with small motors.
 
There is no color code corresponding to wire gauge, but all wire is required to have the type and gauge printed on it periodically or it isn't approved for use in buildings. Frequently that is embossed in, other times it is printed poorly, so it can be hard to spot.

Is the motor a capacitor start...does it have a big ugly bulge on one side that houses a large plastic cylinder with 2 wires attached? If that is going bad the starting current can go up too and cause the symptoms you are seeing.

My Ugly's electrical reference book had a Hp to current chart. It is rough, but it tells me a 1.5Hp motor draws 20 amps. Different efficiencies will change that...sometimes by quite a lot. Anything else you might have plugged into that circuit will put you over the top as well...though the standard household CB has quite a lot of delay already built in.

Anyway, 20 amps over a 60' run gives a voltage loss of:

12AWG-4.6V
10AWG-2.9V
8AWG-1.83V

But that is once it is running at full speed...starting currents are much higher and make the drop much larger. The drop isn't as important as seeing how much going up one little trade size affects the losses.

For what it's worth...:D
 
wow, lots of good info. The runs from the breaker box were 10ga. I found out that the sheathing is "UF" which means you can bury it without a conduit.

I exchanged one of the 12ga ciruits in the shop for 10ga wire, making the whole run 10ga. Then I replaced the 20a breaker with a 30a. Runs great now.

BTW, it was previously tripping just prior to reaching max rpm, about 2-3 secs after hitting the switch. I'm fairly confident the problem was a combination of start draw and length of run.
 
Thank you gentlemen for this great information. I just happen to have the electrician coming next week to wire up the new workshop.
The timing of this post couldn't have been better. :)
 
radius said:
Thank you gentlemen for this great information. I just happen to have the electrician coming next week to wire up the new workshop.
The timing of this post couldn't have been better. :)
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My thanks also. I have a lot of wiring to start next week.:thumbup:
 
radius said:
Thank you gentlemen for this great information. I just happen to have the electrician coming next week to wire up the new workshop.
The timing of this post couldn't have been better. :)
Click to expand...

If at all possible run a heavy 220 to the shop. If you don't need it now you will. I ran 100 amps of 220 to my small shop. Put in a panel and the broke it to 2 20amp 220 and a bunch of 20 amp 110s.

Tito
It should be possible to go back to the source of your shop power, install a 20 amp 220 breaker on one of the 10 gauge wires and then have a 20 amp 220 in the shop
 
ib2v4u said:
If at all possible run a heavy 220 to the shop. If you don't need it now you will. I ran 100 amps of 220 to my small shop. Put in a panel and the broke it to 2 20amp 220 and a bunch of 20 amp 110s.

Tito
It should be possible to go back to the source of your shop power, install a 20 amp 220 breaker on one of the 10 gauge wires and then have a 20 amp 220 in the shop
Click to expand...

It is, but I would have to give something up. Right now, the 4 110v circuits are Left Outlets (4), Right Outlets (4), 1 30A AC Outlet (dedicated to: grinder, wall mount air cond., and outside fountain pump), and a circuit for the lights.

I could sacrifice one of the wall circuits or wire all 8 outlets in parallel. I don't think I will ever run enough equipment on that circuit to trip the 20A breaker on the other end. However it was much faster to change the one circuit of wire at the shop end and throw a 30A breaker in.

I move about every 3 years, so it doesn't make much sense to invest too much into a new shop every time. I just need something safe that I can work with, and minimal time jacking around with it. One of these days when we're settled, I'm gonna build shop-zilla. Until then, I'm counting this as chalking up experience...thanks all for the help. I've been a member here for many years, and the usefulness over time has been priceless.
 
ib2v4u said:
If at all possible run a heavy 220 to the shop. If you don't need it now you will. I ran 100 amps of 220 to my small shop. Put in a panel and the broke it to 2 20amp 220 and a bunch of 20 amp 110s.
Click to expand...

Speaking of the future, this is exactly how I would like to set up my future shop - run one underground cable to a dedicated shop breaker box. That solves 95% of the issues I've faced in the past. Plenty of juice, room for expansion, etc.

I'll be back here when it comes time to switch to DC....
 
tito said:
Speaking of the future, this is exactly how I would like to set up my future shop - run one underground cable to a dedicated shop breaker box. That solves 95% of the issues I've faced in the past. Plenty of juice, room for expansion, etc.

I'll be back here when it comes time to switch to DC....
Click to expand...

That is exactly what I just did. I upgraded to a 2hp motor for my KMG. I did a 220 box so I can also run a dust collector and hopefully some day a heat treat oven.
 
One of my first projects when I moved to the current house is to put in a dedicated garage box. I only used an 8 circuit box fed by a 50 amp breaker...and then hung the hot tub (4 of the 8 circuits because of the huge GFCI breaker) on it. My bad...I should know better. You want at least 16 circuits (more is better) and 100 amps minimum to run any serious number of machines. An A/C, air compressor, and a few others running add up fast.
 
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