PM2000 owners, I have a Electrical question?

[MrAudio815]

Hey Everyone,


It's been a while. Anyway I have been getting electrical out to my garage from inside the townhome. I put 50 amps out there with a 50 amp double pole circuit breaker and 6-3 gauge wire which can handle 55amps.

Anyway my question is I have 12 gauge wire that I used to run my PM2000 tablesaw back in NC which 12 guage wire can handle 20amps, but I have a 30amp circuit breaker. :icon_scra For some reason I thought that's what I needed? I believe I am wrong and just want to make sure that I should have a 20amp circuit breaker.

Thanks guys~!

Also how many circuit breakers can I put in a sub panel that has a 50amp double pole circuit breaker? I have 12 slots minus the 2 for the 50 amp breaker so actually 10 slots and 20 if I use the slim breakers?

I ask because I added up all the circuit breaker amps on my 100amp main breaker and got over 240amps. That for sure should blow the breaker, unless of course not all that power is being used at one time.

Electricain people help?

 

[Bas]

I'm not an electrician, but having recently put in a subpanel, I can probably supply a few answers.

First, your circuit breaker should never exceed what the wire is rated for. So use a 20amp breaker with 12 gauge wire. If you use a 30amp breaker, you run the risk of a fire because it won't trip. The other way around is fine, i.e. you can use 10 gauge wire with a 20amp breaker. Also, the breaker is there to protect the wire, not the equipment. Having said that, limiting the amperage to your table saw by using a 20 amp breaker is not a bad idea.

Second, it doesn't matter what the total amperage of all the breakers in your subpanel is. If I add everything in my subpanel (which has a 100amp breaker), I have almost 400amps. Of course, I typically only run a couple of tools (e.g. table saw and DC) at the same time. As long as the actual load < subpanel's capacity, you're fine.

 

[Mt. Gomer]

Yep, what Bas said. One aditional note: I'd recommend converting any of your larger tools that you can to 240 if for no other reason than to give you a little headroom on your 50A panel. Tools running at 240 will draw roughly half the amps as they will at 120v. When the total available is 50 that can be a very significant savings. When I ran a sub-panel to my basement shop I opted to go 60A rather than something higher becuase it was a relatively long run and I just couldn't afford the upfront wiring costs to go any higher than 60A. Like you I loaded a small panel up with slim breakers so I'd have room to add more circuits later if the need ever arises and I converted my larger machines (Air compressor, TS, BS, DC) to 240v so I'd have plenty of current...

Trav

 

[terry1166]

The National Electrical Code allows the circuit breaker serving a motor load to be larger in amperage than the wire ampere rating. This due to the fact that at the instant a motor starts the amperage load is much higher than the running amps. If you look at the nameplate on an outdoor air conditioning unit you might find that the MCA (minimum circuit amps) might be shown as 30 amperes (#10 conductor) and the maximum overcurrent protection allowed (circuit breaker) is 45 amperes. That being said, better overload protection will be provided by the smallest size circuit breaker that will allow the motor to start. A reasonably solid short circuit on #12 wire would easily trip even a very large circuit breaker. A 240V table saw with a 3 hp motor should have no trouble starting with a 20 ampere circuit breaker. I don't have any motor tables with me at the moment, but a 5 hp, 240V single phase table saw would probably require a larger circuit breaker but possibly only a 20 ampere conductor (#12). The conductor size required can be determined by the full load amps (FLA) shown on the nameplate. My Steel City 3 hp saw operates fine with a 20 ampere breaker. The motor full load amps is shown as 12 amperes.

Terry Davis

 

[MrAudio815]

I'm not an electrician, but having recently put in a subpanel, I can probably supply a few answers.

First, your circuit breaker should never exceed what the wire is rated for. So use a 20amp breaker with 12 gauge wire. If you use a 30amp breaker, you run the risk of a fire because it won't trip. The other way around is fine, i.e. you can use 10 gauge wire with a 20amp breaker. Also, the breaker is there to protect the wire, not the equipment. Having said that, limiting the amperage to your table saw by using a 20 amp breaker is not a bad idea.

Second, it doesn't matter what the total amperage of all the breakers in your subpanel is. If I add everything in my subpanel (which has a 100amp breaker), I have almost 400amps. Of course, I typically only run a couple of tools (e.g. table saw and DC) at the same time. As long as the actual load < subpanel's capacity, you're fine.

Thanks BAS,


I new that the circuit breaker is supposed to be equal too or less than what the wire can handle, that's why I was confused on why for some reason I was thinking I needed a 30amp breaker? :eusa_doh:

Thanks for the help~!

 

[drw]

I do not want to steal this thread, but I often read on this site references to voltages of 220, 240 and occasionally 230. While the numbers certainly aren't the same, do they in fact reference the same thing?

Cheers,
Donn

 

[Mt. Gomer]

I do not want to steal this thread, but I often read on this site references to voltages of 220, 240 and occasionally 230. While the numbers certainly aren't the same, do they in fact reference the same thing?

Cheers,
Donn

Yep and I honestly can't keep track of which on is technically correct (I think 120v and 240v but don't quote me on that). For our purposes here they are generally used interchangebly. Just think regular voltage ( 110/115/120, one hot conductor) or higher voltage ( 220/230/240, two hot conductors). I believe currently (no pun intended) the US is standardized at 120/240... however it changed from 110/220 at some time in the not terribly distant past so a lot of people still use the old numbers...

Travis

Edit: Here's a quote from wikipedia....

Standardized at 120 V. Electricity suppliers aim to keep most customers supplied between 114 and 126 V most of the time. 240 V/60 Hz used for heavy duty applications such as air conditioners, clothes dryers, stoves, ovens, and water heaters. Buildings with more than two branch circuits will have both 120 and 240 V available. Since 1962, Type B outlets are required by code in new construction and renovation. A T-slot Type B is rated for 20 amperes for use in kitchens or other areas using large 120 V appliances.

 

[drw]

Thanks Travis...while I thought the numbers were being used interchangeably, I am often caught by what I had assumed to be true.

Cheers,
Donn

 

[erasmussen]

My voltages here actually measure 123/246 thats with a factory calibrated fluke 26 II

 

[cpowell]

Yep, what Bas said. One aditional note: I'd recommend converting any of your larger tools that you can to 240 if for no other reason than to give you a little headroom on your 50A panel. Tools running at 240 will draw roughly half the amps as they will at 120v. When the total available is 50 that can be a very significant savings. When I ran a sub-panel to my basement shop I opted to go 60A rather than something higher becuase it was a relatively long run and I just couldn't afford the upfront wiring costs to go any higher than 60A. Like you I loaded a small panel up with slim breakers so I'd have room to add more circuits later if the need ever arises and I converted my larger machines (Air compressor, tablesaw, bandsaw, DC) to 240v so I'd have plenty of current...

Trav

If you balance out your 120V loads on the panel so that the running current load on each 120V leg is about the same then you will get about the same benefit as if using mostly 240V loads.

Running higher voltage motors allows you to downsize conductors, saving on wire costs. And of course 240V motors usually means more HP than 120V - and that's a good thing, right? :gar-Bi


Chuck

 

[dlrion]

Tesla was the pioneer of AC and set 110 and 220, I think it's because it is easy to remember, if I recall correctly, Edison HATED this and was a huge proponent of DC electricity, trying to scare the public away from AC by electrocuting elephants and such with AC.

I think they changed it officially in the 1970's to 120 and 240. The power company is ALWAYS off... by as much as 6 or 7 volts... I don't really know why, but I have seen my Dad measure for years, and it's never accurate.

As Earl can testify, 10 volts makes a difference.

Military is the only one who uses 115/ 230 officially in the US.

It's really a pain...

and who set 120 240??? why not simply 100 or 200?

 

[MrAudio815]

Yep, what Bas said. One aditional note: I'd recommend converting any of your larger tools that you can to 240 if for no other reason than to give you a little headroom on your 50A panel. Tools running at 240 will draw roughly half the amps as they will at 120v. When the total available is 50 that can be a very significant savings. When I ran a sub-panel to my basement shop I opted to go 60A rather than something higher becuase it was a relatively long run and I just couldn't afford the upfront wiring costs to go any higher than 60A. Like you I loaded a small panel up with slim breakers so I'd have room to add more circuits later if the need ever arises and I converted my larger machines (Air compressor, tablesaw, bandsaw, DC) to 240v so I'd have plenty of current...

Trav

Well I just went to the Powermatic website and saw under specifications that the PM2000 has 13amps, I guess for some reason I got confused and thought 30amps. I guess both have a 30 in them.:eusa_doh: Gonna go get a 20 amp breaker and return the 30amp breaker~! :gar-Bi

Anyway Travis,

You said you opted to go with 60amps for your sub panel, what size wire did you use? The reason I ask is when I was in lowes they had 6 gauge wire and by it, it said 55amps, and 4 gauge handles 70amps? So I am just wondering how you got 60amps?

I'm running the 50 foot 6-3 gauge package from lowes.

Please help me understand how you got 60amps? Thanks~!

 

[Mt. Gomer]

If you balance out your 120V loads on the panel so that the running current load on each 120V leg is about the same then you will get about the same benefit as if using mostly 240V loads. Chuck

I'm a little slow when it comes to this kind of thing so I had to think about this one for a few minutes :icon_scra... but... yeah, you're right on. For those who are slow like me (and, like me, interested in understanding why/how this all works) here's how I sorted it out in my head. Ya'll who know better can correct me if I get this wrong.

Say I had a 50A/240V subpanel, that would mean I have two legs of 120V each connecting to one side of a two pole 50A breaker (meaning each leg can have up to 50A running before it trips). Into this box I install 4 20A Circuit breakers, 2 on leg A and 2 on leg B. Even if I managed to load each circuit to a full 20 A (yes I know this isn't possible in the real world but just using whole numbers for the sake of clarity) each leg of the box would only be carrying 40A (on a 50A breaker). Sooo, that means I'm running 80A total on a 50A subpanel. Very cool. :icon_thum

Thanks Chuck!