softening the startup load on my table saw?

Greetings Dan, It it was me I'd use your suggestion. Easy enough to wire. In fact, contactors can be had with switches that turn off another contactor to prevent plugging. When I put a new control on one of my mills I did exactly this. And all the power coming from the motor does eventually end up in the shop. Eric

motor does eventually

Many years ago, I suggested something similar. The Navy had a building wit h large electric heaters and a large air compressor. When both heaters and the air compressor were on, it exceeded the ratings of the transformers th at supplied the building. The Navy just swapped out the power transformers for larger transformers.

Dan

You should enquire about 3 phase as a mate that used to live in Munich said it was very common to have a 3 phase supply in a domestic house as he did. Apparently rather than spread the phase loads between different houses as is done in the UK, and I think the US, he said the different floors were fed the different phases to balance the loads. Another who posts here from time to time mentioned the same about 3 phase in houses in Germany and was quite happy he could run a good sized 3phase welder IIRC at home. My mothers old house in the UK had 3 phase because the previous owner that built the house thought some of their garage units could be used for light industrial use. They said the only additional cost at the time was the 3 phase cable compared to single phase, no problem getting it connected although it was never used the house only had a single phase meter, at least the 3 phase was at the house if needed.

OK, this explains the problem! Note that most induction motors draw a current close to the full rating even when idling. This current is at a very lagging power factor, so the true wattage is small, but the current is large. As the load is increased, the phase angle changes, so greater wattage is drawn although the current reading only increases slightly. The breaker only senses current, and not power.

So, your 14.5 Amp motor most likely draws about 12 A with the saw idling, and could be 60+ Amps during the start. Obviously, you can't run more than a small light bulb on the same circuit at the same time without risking tripping that 16 A breaker. Especially if it is a standard breaker, and not a motor-load breaker.

You may be able to do most of the work (drilling holes, installing conduit, etc.) and then just have the licensed electrician make the final connection. You might save some money that way.

Jon

I missed the 230 volt reference - What amperage circuit is he on??? Virtually never see 15 amp 240 around here - very occaisionally see

I take it this is a european setup?? Or british? Never see "16 amp" breakers in North America. If so, it is line to neutral, not line to line like here in the Americas. Get a SPDT switch or contactor and wire it so the saw and the heater can NEVER be on at the same time..

We run 10 inchers on 115 /120 over here.

I have a large Milwaukee grinder that pops a 20 amp breaker. To use it I have to put a extension cord in series with the grinder. Also the cord has to be a thin one to cut down on the starting current. The breaker is brand new and this happens on several different circuits.

John

Try putting an extension cord in series with the machine. There will be enough current limiting with a light duty cord.

John

My well/pump and my drill press/lathe/mill VFDs are on 15A 240 circuits. They're common enough that HD/Lowes carries them. My "here" being Massachusetts. Bob

Thanks for more suggestions. Yes, I'm in Germany where your standard box ha s 16 amp breakers and 230v, line and neutral. Many newer houses and buildin gs also have 1 phase 400v, which is mainly used for instantaneous water hea ters (which I hate!). There may be three phase some places, but I've never seen it.

As for my problem, I'm surprised I'm not having more trouble than I am. I d on't think I've ever blown the breaker when starting the table saw if the h eaters are off, and it usually doesn't happen if only one heater is off. Th at means I'm pulling like 5.3KW!

Interesting the idea of running a long extension cord. I always thought tha t the opposite was true - that more copper, not less, is easier on the brea ker. At any rate, I think I'm sort of doing that already. The wires are pre tty thin - the space having been a garage before, where only lighting was e xpected. When I was running almost everything from one receptacle, and I no ticed that the wire to it was getting warm. Now that I've spread things out that's no longer evident.

I think that I can get the guys to agree to let me do the runs for new circ uits as long as I hire an electrician to connect everything up. That is wha t I'll do. In the mean time I just have to be diligent about shutting off t he heaters when using the saw. I don't use it all that much anyway!

Interesting the idea of running a long extension cord. I always thought that the opposite was true - that more copper, not less, is easier on the breaker. At any rate, I think I'm sort of doing that already. The wires are pretty thin - the space having been a garage before, where only lighting was expected. When I was running almost everything from one receptacle, and I noticed that the wire to it was getting warm. Now that I've spread things out that's no longer evident.

Resistance in the wire prolongs the time the motor's start windings are engaged, possibly enough to overheat them.

There you have it. Don't underfeed your machines. They need clean, healthy amps, and lots of 'em!

I think the guy who suggested that did so because it worked for him with a big angle grinder. The grinder has a universal brush motor, which is perfectly happy running on reduced voltage, and reduced power output. Your saw presumably has an induction motor, which isn't nearly as forgiving. It will likely draw more current at a lower voltage - look at the nameplate on a 208-230/460 volt motor for a real-world example:

No, in my case it was an old Beaver table saw with a 1hp Lehland repulsion start induction motor (one that has brushes for starting)

The post I had in mind said, "I have a large Milwaukee grinder that pops a 20 amp breaker. To use it I have to put a extension cord in series with the grinder."

Because the start-up surge for a repulsion start/induction run motor is smaller than for a straight induction motor, I've heard they were often used in rural areas with long or marginal capacity feeds, much like an undersized extension.

But, once up to speed, I'd expect a repulsion/induction motor to draw more current as the voltage sags, just like a regular induction motor. Maybe that's part of the reason, besides added complexity, they're typically so big - so they'll tolerate undervoltage and the resulting higher current.

My compressor has a 5HP repulsion start/induction run motor on it that's bigger than a modern 15HP motor. It's strapped for 230V, but can be reconnected for 115V.

We always used repulsion start motors on the bale elevators on the farm, They could start with a load of bales - a 2 HP would start a heavier load than a 5 hp cap start.

TWO. One for the heaters, one for the saw.

Most Euro power is 230v with 16 amp breakers.

Two would be nice, three better. One for heating, a second for the saw, and a third for everything else.

I've discovered that 3 phase is actually common in Germany, but it's differ ent. Since each leg is 230v to neutral, then I presume that between legs it is around 460v. So, normally you don't have any two legs coming anywhere n ear each other. In a private house you might be able to access 3 ph. but no t in a building, unless you want to pay for some expensive electrical work.

In my case, I'm running power from a secondary box in the courtyard behind the main building. That's almost certainly only 1 ph. I can add a couple ci rcuits from there, but I wonder if the box itself can handle the draw. The idea of a cutout relay on the heaters now looks worth exploring.

As things stand, it's only the combination of the saw and heaters which is creating problems. With the heaters running, I can still run the lathe, lig hts, and small machines without trouble, so at the moment there's no need t o load up a trebuchet with stacks of Euro notes to attack this inconvenienc e!