I've discovered that I can't increase our 200 amp service for a reasonable price. The 400 amp panel and installing it is easy and low cost (relatively), but changing the breaker on the pole and the 200 feet of underground wire that is not adequate for 400 amp is not. We're in a rural area and the electric co-op requires the breaker under the meter at the service entrance.

The reason for increase the service is to use a large welder, stamping press, and demand heater in a shop area, but not simultaneously.

I know it's possible, but I can't find the contactor or relays I need to do this.

I'd like to have the energizing of the large 19.2 KW load cut a 10 KW and/or an 8KW load. The 19.2 load is the demand heater connected to two 40 amp breakers (it has two separate circuits), 10 KW load is on one 40 amp, and the 8K load on a 30 AMP breaker.

If there's an easy mechanical way to do this, my problem would be solved.

Essentially, the 10 KW load and the 8 KW load (for a large well pump at 900 feet or so) are interruptible at any time as neither has any safety or convenience issues if they are off for the 90 minutes or so per day, but not continuous, that I actually need the 19.2 KW for heavy shop work.

I'm thinking that a normally on contactor in the 10 KW 40 amp and 8 KW 30 amp circuit that would go OFF when the 19.2 KW load (either of the two circuits) is energized.

All load control items that I can find seem to be hugely expensive and for use only by the power company.

Thanks!
MH

When reading your description, something is amis. In the instant the Welder is energized the other loads may actually be on. Would this be a problem?

Would something as easy as three mechanical disconnects and a timer suffice. Something like connect welder, push timer; timer buzzes in 90 minutes to remind you you have to turn the pump on for a while.

I'm thinking out loud a bit. You might be able to do something like use a disconnect with an auxiliary contact(s) for welder. With the welder disconnect off, power can be applied via a contactor to the other loads. When the welder disconnect is moved to the on position, power is cut to the other loads. You could start a 90 minute timer to remind you to put the switch back.

This makes the duty cycle smaller.

If you have a way to determine whether the welder's main breaker/power switch is on, your half way there. You might be able to replace that breaker with one with an aux contact that will allow you to determine the position of the breaker.

You don't have to duplicate the removal of power. For the pump, you just need to tap into the control circuit. Maybe the same is true for the heater as well.

These are just some ideas and stuff to think about, not an actual solution.

Contactors and such:

Motor Controls Products

Thanks for your resonse

KISS When reading your description, something is amis. In the instant the Welder is energized the other loads may actually be on. Would this be a problem?

That is not a problem as the 1/20 of a second or so the slowest contacter take would not cause a problem.

KISS Would something as easy as three mechanical disconnects and a timer suffice. Something like connect welder, push timer; timer buzzes in 90 minutes to remind you you have to turn the pump on for a while.

KISS I'm thinking out loud a bit. You might be able to do something like use a disconnect with an auxiliary contact(s) for welder. With the welder disconnect off, power can be applied via a contactor to the other loads. When the welder disconnect is moved to the on position, power is cut to the other loads. You could start a 90 minute timer to remind you to put the switch back.

That is exactly what I do now, and is a great, simple, and elegant solution. Unfortunately, the elec. code will not allow for the use of electricity by a person with a brain, so this cannot require manual intervention of any kind nor cause a "life threatening" situation like the well pump not being run automatically.

KISS This makes the duty cycle smaller.

KISS If you have a way to determine whether the welder's main breaker/power switch is on, your half way there. You might be able to replace that breaker with one with an aux contact that will allow you to determine the position of the breaker.

KISS You don't have to duplicate the removal of power. For the pump, you just need to tap into the control circuit. Maybe the same is true for the heater as well.

KISS These are just some ideas and stuff to think about, not an actual solution.[/QUOTE]

I appreciate your ideas; I don't usually know what mine are until I say them, usually around someone who know a log more than I used to think I knew.

Mark H.

You could have 3 contactors, Double Pole/ Double Throw. Have the pump be main Importance, When Pump contactor is energized, it lifts power to other 2 control to other contactors, so no 2 can be on at the same time. You would need to get an extra wire from load side of power switch to each item, first one on gets power, other 2 cannot as power is lifted as contactor is energized. But wire so when you turn equipment off, Pump will have
Power.

Thanks. I believe that is what I am looking for.

Since the well pump and boiler are NOT most important (don't thing I'd empty the 400 gallons of water remaining in the cistern when the pump would normally start nor would the heating boiler cool at all in 20 minutes or so of welding), I think I'll do something similar to your suggestion.

That is, pump contacter and boiler contacter are normally closed and are lifted when the shop load comes on and energizes the contactor.

With 240 volts, is a DPDT with a common neutral bypassing what should be used? Or do the legs AND the neutral need to be disengaged by Triple Pole Double Throw?

The county inspector is a bit vague about this. Since he works for the county, he must have unlimited $$$ as he feels it would be easier to replace the pole switch, the panel, and the underground wiring! I think not.

Thanks!

I would use 120 volt contactor coils, they would get power when other contactor relaxes, or disengages when this energizes. The way I am thinking, was to use the Power switch load wire(after switch)

You don't switch the neutral.

You can make low voltage control wires though, using say a 120 to 24 VAC step-down transformer. Just can't run the low voltage stuff in the conduit with the high voltage stuff.

If you need to, ABB SSAC Timers & Controls Fast Facts (800) 377-SSAC(7722) has current sensors. You can detect current draw and get a contact closure out.

You never really mentioned the relative locations of the power feed to these units. Do they all come from the same panel? If they do, then life is somewhat easy.

I can talk you through using DIN rail making of a panel.