[OP]
Member
I'm about to refurb a PM66 table saw and I need a new power switch. Was thinking of going with the linked aftermarket power switch rather than the PM one to save money.
https://www.amazon.com/Big-Horn-1882...pd_rd_wg=HlYIW
My only concern is that my motor is a 15 amp motor and the amp range on this switch is 18-26. Will this damage my motor or present any problems?
Along with that idea, I can't find electrical specs on the replacement PM mag switches so I can't verify the amperage numbers.
Contributor
It will work fine but it will not protect the motor from a long continuous slight overload that will slowly overheat the motor. Like from ripping thick hardwood for an hour. If there is a short it will work fine.
Has you saw ever tripped the overloads? Mine never has.
Bill D
[OP]
Member
I don't expect to be doing work that intensive, would the thermal protection built into the motor kick in at that point and do the protecting?
I also just found that the PM replacement mag switch is also rated at 18 amps so I don't really see any other option other than building a switch from scratch, which so far doesn't sound like its worth the time or effort.
A 15 amp breaker in the sub panel I know would trip before it reached that point as well, but I was planning on putting in a 20-amp 230v breaker for the extra head room and to future proof myself. Would it be better to have the 15 amp breaker instead?
Member
I don't believe the switch is intended to provide motor protection other than preventing the saw from restarting unintentionally after a power interruption.
Contributor
The linked switch has an adjustable overload that can be varied from 18 to 26 amp. It is the green wheel pointing to 22amps.Originally Posted by Rege Sullivan
Contributor
It looks like Bighorn just puts their name on it. Here's one sold by BlackJack that is rated for 12 to 18 amps made by the same Taiwanese company. They appear to be just sold in Canada though. I'm sure if you search around a little you can find one sold in the US (unless you live in Canada) that would also work. I think another brand is NHD that looks like a copy or made in the same factory in Taiwan. If you are going to pay for it you might as well get the full benefits from it.
[OP]
Member
Thanks for the find, it does look like they ship to the US but it brings the price up for sure.
Contributor
I used the Grizzly switch when facing this same problem. Worked great. Not sure what the current offerings are.
Rustic? Well, no. That was not my intention!
[OP]
Member
So can a 3 phase switch be used with a single phase motor? That would put the amps in the proper range. That's what the workshop supply link implies in their description and this link to a 3-phase switch seems to be exactly the same as the one in the work shop supply link...minus the stop switch.
https://www.amazon.com/Big-Horn-1883...pd_rd_wg=JoMD3
Last edited by Dolfo Picanco; 09-20-2020 at 2:51 PM.
Contributor
Yes but you need to pay attention to the wiring. Since you will only be using 2 or the 3 terminals on the contactor it's possible to use the one that's not connected to the magnet. The directions should tell you which terminals to use. The other possible issue could be the thermal overload. It looks at all 3 phases. The less expensive ones just look at each phase and as long as they are all less than the cut off current they are happy. More expensive ones also look for a phase imbalance. I think the Bighorn one is the same as the NHD brand. Here's a link to one on ebay that has a chart showing that the MS1-12D3220 will work for a 3hp single phase motor or a 3 phase 5hp motor.
[OP]
Member
Man, so many variables and all because my motor seems to be on the lower amperage for a 3 HP. I'd love to save the money but it might just be worth the extra $20 to buy that one on ebay.
I noticed the Big Horn 3hp 1ph switch has a notch below 18 on the overload protection, would that actually take it below 18amps?
[OP]
Member
Is it better that it looks at each phase or an imbalance? seems like if it's wired for a single phase then you want one that looks at all each phase because one that looks at an imbalance would trigger it to shut off. or am I still missing something?
Contributor
The phase imbalance is only for 3 phase equipment. One of the problems we have where I work is the terminals where wires connect to things like motors aren't always as good of a connection as they should be. Eventually that terminal will overhead which will cause the resistance to increase. This will cause the current in that phase to drop. For us it's better to know ahead of time and repair the problem, that's what a thermal overload with phase imbalance would tell you. If we don't catch it in time what usually happens is the terminal will melt and destroy the wires around it. If it's the connection on a motor it'll have to be replaced. A thermal overload without the phase imbalancer would just look for any one of the three phases being higher than what the cut off is set to. One other thing we do is remove the covers to wire connections and scan them with an IR gun looking for excessive heat. I doubt it's anything to worry about with the switch you are looking to buy. The only reason I brought it up is that if you didn't know about it and you did have a magnetic switch with it included it would cause you plenty of head scratching trying to figure out why it's not working.
[OP]
Member
So I'm correct in the assumption from my previous post? I got an answer from the BigHorn one on amazon saying that there are people who wired it up to a single phase motor and it works, which would mean the overload circuit looks at any of phases for the amp limit, which is what I want in this sort of set up?
Contributor
All? my starters are three phase and I have no three phase power in the shop. I just use two of the contacts and ignore number three. Just watch the coil voltage and make sure you have that voltage available. 24, 120,208, 240, 340 volts are common. On the bay a used three phase starter tends to cost less then a single phase unit.
Bil lD
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