Wiring Up a PRTalpha

[porscheman]

Hi everyone - I recently “joined the ShopBot Nation" (FINALLY!!!) when I purchased a lightly-used PRTalpha 4x8 machine, equipped with dual Z's - Columbo 3HP spindle and PC router. I've been methodically going over it all, cleaning/reassembling/aligning the Bot and learning about the myriad of machine details in the process. Now I know what fun, and occasional frustration, all the members of this forum have been enjoying while I've been "lurking" over the past few years.

Anyway, I'm at the point where I'm ready to wire the Bot into my electrical panel. Actually, that statement isn't accurate since I'll have an electrician do the work in the main panel, but I'm confident I should be able to rough in the wiring and make the other connections before the circuits go live. This will save me a considerable amount of money given the going rate for electricians in my area. I've done plenty of electrical wiring work in my home/shop before and I'm comfortable doing this kind of work. However, there are a few questions I wanted to ask for those of you that have gone down this path before me.

The manual states that I need a 40A/220V (single phase) circuit for the spindle power and a separate 30A/220V circuit for the control box and router. Each of these service lines should have a fused disconnect located in relatively close proximity to the Bot. All of that makes perfect sense to me, but several questions do arise:

1) For each of the electrical service lines, should I buy a matching amperage circuit breaker for the main panel as that specified for the fused disconnect? For example, do I use a 40A breaker in conjunction with a 40A fused disconnect for the spindle, or do I want to “oversize” the breaker (move it up to 50A) so that the fused disconnect serves as the “first line of defense”? Asked another way, do I want the breaker in the main panel to trip first or do I want the fuses to burn out? Obviously, I don’t want either of those situations to ever occur, but these devices are in place to protect the equipment and I want to specify them correctly.

2) Should the fuses in the disconnect boxes be the “time delay” cartridges used for protection of electrical motors or should they be a standard “general purpose” fuse? Obviously the spindle is an electric motor, which suggests a time delay fuse, but I don’t know for sure. Similarly, do I want a time delay fuse to protect the control box/router?

3) And finally, I have to ask a question that seems embarrassing because of all the previous wiring that I done, but until this application (i.e., the installation of fused disconnects) I hadn’t really considered this specific issue before…. What I’m referring to is the amperage size for the pair of fuses used in each disconnect box. In the many other 220V woodworking machines that I’ve hooked up, the notion of supplying two 110V “legs” to achieve the 220V rating has always made sense – these legs were connected to a properly rate breaker in the main panel. However (and here’s the dumb question), does each 110V leg also supply only half of the total amperage as well or does it carry a full amperage load? For example, in the 40A service going to the spindle, is each fuse in the disconnect box a 20A fuse, which combine to give me 40A of power/protection, or does EACH of those fuses have to be rated at 40 amps?

Answers to these questions should allow me to have the installed services lines and breakers ready for my electrician to inspect/install at the main panel, thus saving my dollars for all the cool software and Bot accessories that are pulling at my wallet.

Thanks in advance for any replies. Regards.

John

[thewoodcrafter]

Sounds like you are close to making saw dust.
Congrats!
I think I can help a little.

#3 FULL load. 2 - 20AMP fuses don't give you 40AMP only 20AMP. So use 40AMp fuses.

#2 I would use the one time fuses,, cheaper. I think you are way over on the AMP anyway so a short startup spike will not blow the fuse.

#1 The breaker should be sized for the wire, you don't over size unless you are running several hundred feet. Then the wire is bigger also.

Sounds like your Amperages are big.
I have the same setup and I ran a 50AMP sub-panel to the Bot and ran all my circuits from that.
20AMP for the VFD, 20Amp for the Bot control panel , 20AMP for the router and 20AMP for my dust collector. My shop has gotten to 102F and I have not had anything trip.
It may be cheaper running a sub-panel. I only have a fused disconnect on the VFD.

[Gary Campbell]

John...
Roger has you going in the right direction, let me add a couple clarifications:

The fused disconnect is a safety item. I has to be neither a fuse or a disconnect. It can be a breaker and an outlet with a plug. In any hardwired appliance(ShopBot) you need a service disconnect for the safety of the repairman. If your machine is located in fairly close proximity to the machine, a simple breaker in the panel, or sub panel will do. It cannot be in another room. If the panel is in another room, you can use a plug near the machine, and have the breaker in the other room.

If you have to buy a breaker, buy the recommended size. i.e. 40Amp double pole for the 40A circuit, code requires they be connected to act as one. As Roger says, size the wire to the load.

Most standard breakers are built as time delay for average type resistive/inductive loads. It would be rare that you would need a special purpose item for the Bot.

Gary

[porscheman]

Roger/Gary,

Thanks for the quick replies - everything seems in line with my general understanding of the wiring parameters. I'm definitely familiar with the need for sizing the breakers to the wiring size - just didn't know if I wanted to avoid having the breaker trip first instead of the fuses in the disconnect box.

Then my (sometimes slow-acting) brain reminded me that my actual "first line of defense" in protecting the spindle and router are the fuses in the control box itself. Again, I don't want to see them ever blown, but they are there to protect my investment, along with properly sized wires/fuses/breakers further back in the supply line.

Regards.

John

[dana_swift]

John- the term "fused disconnect" does not mean to imply you should only use a fuse. Circuit breakers are a better choice for all but a few specialized applications.

As I just posted on another thread- the advantage of a dual 220v breaker is if one side develops a fault, BOTH sides will be turned off. Much safer when things have gone wrong.

You are so close to having this thing up and going! Then we will get to hear from you more as you figure out all the ins and outs of it-

Welcome!

D

[porscheman]

Dana,

Thanks for the response - I read that other posting with great interest, especially the part which mentioned having the two legs of the 220V circuit 180 degrees out of phase with each other, providing "smoother" power than the equivalent 110V circuit (hopefully I worded that correctly).

My question is how the two legs of the 220V line are placed out of phase with each other - does this happen inside a double pole circuit breaker in the main panel? I can't imagine that would be the case, but it is electrical "nuances" like this that are beyond my current skill level (and why I'm posting questions in this forum). In the past, when I've wired 220V circuits, the red and black legs are routed into the same double pole breaker, and the white/ground wires go to the neutral bus (which is the same as the ground bus in all my main panels). In some instances, the neutral wire is ommited and there are only two hot legs and the ground. So, once again, what is needed to shift the phase of the two hot legs, or does this somehow occur "automatically"?

And finally, regarding the comment on not just relying on the fuse for my means of protection, I think I should have several lines of defense. First, I'll have a 30A breaker in the main panel, followed by the fused disconnect, and then further protection from the fuses within the SB control box. It doesn't look like the control box has a built-in fuse of it's own to protect the drivers/motors. Obviously, the fused disconnect boxes have the disconnect mechanism that can be removed when servicing the machine (or in an emergency).

As you say, I can't wait to finally get this bad boy up and running and try machining some of amazing examples that have been presented on this forum. Though it's been stated by many other postings on this site, this forum and the general information sharing within the ShopBot community is the principal reason that I bought this brand of CNC. Special thanks go out to David Buchsbaum, who lives close to me and has spent countless hours helping me to learn more about the ShopBot universe.

John

[dubliner]

As Dana will hopefully agree with me, the phasing is automatic by virtue of the double pole breaker spanning both legs of the line, the lugs alternate from phase to phase & a single fits on one. A double can only go across two. There is a divider fin that prevents you stabbing a double onto two lugs from the same phase.

[dubliner]

John, you can't put a double pole breaker across the same phase, they are only designed to span two phases. Well lets say it would be very hard to...

[richards]

John,

Here in North America, the power company normally supplies 240VAC power by giving you two 120VAC legs that are 180-degrees offset. Most electricians wire your home so that half the lights and outlets are wired to one phase and the other half of the lights and outlets are wired to the other phase. They wire your 240VAC appliances to use both phases.

If you have 240VAC single-phase equipment in your shop, you'll use both phases. If you have 120VAC equipment in your shop, you'll use either half of the power supplied to you from your power company.

You use a fuse to protect the wiring. If you have 12 gauge wiring, you must use a fuse that blows if more than 20A is drawn from that circuit. If you use 14 gauge wiring, then the fuse must blow if 15A is drawn from that circuit. The fuse protects the wiring from getting too hot. It protects you from burning down your shop or house.

Normally a fuse is guaranteed to blow at anywhere from 75% to 100% of the rated current (depending sometimes on the amount of time that the circuit is passing the rated amount of current). In other words, a 20A fuse might blow at 15A and still be considered to be a 20A fuse. The fuse does not pass 20A, instead, it restricts the circuit to 20A or less.

[beacon14]

What makes you think I have not been counting up the hours?

The fuse in the fused disconnect would be redundant at the least and another source of problems at worst. If the wires and breaker are properly sized, and if you have a way to disconnect power to the machine (breaker in the panel box within sight of the machine, or a plug as has been suggested) then there is no need for a separate fused disconnect.

And unless you have more than one service entrance cable from the power company you only have one main panel, the rest are subpanels. The ground and neutral busses should only be bonded at the main panel, never in a subpanel, to avoid ground loops.

[porscheman]

Neville/Mike,

That's an excellent description/supplement to my basic understanding of the phase offset in my circuit breaker panel. I pulled off the cover and took a look at the two blank blank spots where the new double pole breakers are going to go. Now that I know a bit more about what I'm looking at, I can see two "power busses" (probably the wrong term) that zig-zag or alternate their way vertically up the back of the panel. So as you described, when I plug in a double pole breaker, I'll get a connection onto each of those busses - now I know that those 120V legs are 180 degrees offset by virtue of how the breakers clip in. Wow, I buy a ShopBot and get an improved education in household wiring as a side effect. Now all I have to do is put my tongue on both legs at the same time to verify the phase offset.... (VERY bad joke!!).

Everything else mentioned has already been implemented - breakers sized to protect the wiring gauge and wiring sized to handle the amperage loads.

David, regarding the actual need for a fused disconnect, my bot will temporarily live in a location that is not within sight of the breaker panel, so some kind of disconnect was needed. It was less expensive to put in a fused disconnect box ($14 for box and fuses) than to purchase a 30A four-wire plug and receptacle. Plus, I'm "officially" following the instructions in the ShopBot manual (which stipulates the fused disconnect), though all the previous comments which mention why you wouldn't necessarily need to do it that way are perfectly logical. The redundant fuses as a possible source of problems is something I'll definitely keep in mind.

Thanks again to everyone that has chimed in on this topic - hopefully this thread will add to the ever growing knowledge base on the SB forum.

John