Breaker booster ideas

[numerobis]

The plug for my table saw shares a circuit with a few other things, so sometimes I pop the breaker when I turn on the saw — it never pops while I’m using the saw, it’s clearly the j rush current exceeding tolerance on the circuit.

Short of running a dedicated circuit, is there an easy way to put in a capacitor or a battery that can provide that inrush current and keep demand on the circuit sufficiently low?

 

[Defenestrar]

You probably already have a capacitor on the saw motor. It's possible that it's going bad which is what causes the saw to take so much from the line right at start. They're usually not too hard to replace, but it does depend on the motor.

But I also have to pay attention in my shop on some circuits. I know that when I'm close to the load I have to carefully select which order I start things up in (saw, dust collection, lighting, etc...).

 

[GaitherBill]

Have a qualified electrician install a couple more 20 amp circuits.

 

[AmigaPhreak]

Buy an external soft start for your power tools.

Here's an example:

https://www.raymondinnovations.com/products/gs10
You could probably make one too, if you're an electronics person.

 

[KingKrayola]

Are breakers available in the US with different inrush curves? There are three or four different specs in the UK for reactive loads, might be worth a look?

 

[Defenestrar]

They make them. I don't know how much flexibility code has for residential variance.

 

[m0nckywrench]

Defenestrar is on point. How old/cheap is the saw motor? (I use a lot of fossil motors and replacement is expected.) Starter cap deterioration (capacitance loss) is common and they're cheap enough to replace for giggles. There's some leeway but do not go smaller in capacitance. Higher voltage rating is fine but will make no performance difference. There is ample info online covering starting caps and soft start units.

 

[azazel1024]

No updates in a awhile on this.

There are different breakers available. The typical breaker is a magnetic/thermal breaker. It'll trip at whatever its rating is (IIRC, 50ms for most).

An example is Eaton's time chart.

https://www.eaton.com/content/dam/e...elboards/br-family-trip-curves-tc003002en.pdf
As a heads up, if the saw starting is tripping the circuit, try replacing the breaker. NOT with a higher rated breaker, same name plate rating. A worn breaker typically reduces its trip time. That is a good place to start.

But as you can see from their chart, you are talking about 30ms trip time at 600-1500% current (short circuit). You are talking around a minute of capacity at 200-300% current. Now if the saw has a short in the windings, it is possible the inrush current is greater than this range, but you should still have several seconds of load capacity even at the top end of this range on the breaker.

The short version is, there is a problem in the saw, or it is a worn breaker. Or the circuit is being run near max already. Even at 400% of rating, you've got around 5-6s as the minimum trip time.

Eaton's figures are pretty similar to Siemens and other magneto-thermal circuit breakers from my experience.