Cord sizing from 003 to motor

[bsorcs]

For the moment, I want to try powering a 3ph scroll saw [in the process of bringing it back to life] with the 003 and am wondering what cord/plug set up to use. I will use the cord, in some fashion, in the future in a shop as well...eventually. The saw was built in July 1942 and is powered by a Howell 1.5 hp induction resistance motor, the plate of which reads: frame A225; type SC; 855 rpm; 220v, 6.1a; 440v, 3.0a; code = H; and RLS = 40.

208v inrush calculated using the Reliance site [thanks, Speddmon] is 26.2 - 29.5a. I am guessing that a run limit switch is incorporated in the motor, based on the plate, and that this is the reason that the Air Force slapped a "40 AMP" sticker on the SquareD 3-pole start/stop switch that it installed at some point in time. I'd like to wire a female plug to the saw and fab a cord to connect to the 003 using a locking plug/receptacle. The cord is the question. Actually, I suppose that both plugs and cord are the question. Given the calculated inrush, do I have to cover the 40a limit in both plugs and cord [seems extreme] or do I just have to account for the ~30 amps? Staying with SEOOW, 12/4 will cover 20 amps; 10/4, 25 amps, 8/4, 35 amps, and 6/4 gets me 45 amps. Cord run will be 20-30 feet. For what it's worth, the former supply wire in the flex conduit looks like stranded 12AWG; the wire from the switch to the motor looks like solid 12AWG. Surely the AF could not have been wrong?!?

Thoughts??

bill

 

[Triple Jim]

From the spec you posted, it looks like the motor will draw about six amps per phase when putting out its rated power. 12/4 should be plenty. Take a look at this chart:

http://www.engineeringtoolbox.com/three-phase-circuit-wiring-d_737.html

 

[steelandcanvas]

The Air Force had wired that machine correctly.The proper receptacle and plug set-up would be 125/250 Volt, 3 Pole, 4 Wire, Grounding. NEMA #14-20R & 14-20P would be the correct straight blade receptacle and plug. NEMA #L14-20R & L14-20P are locking receptacles and plugs. (Twist-Lock) For cord connectors, change the "R" to a "C". 12-4 is the appropriate cord size, as Triple Jim indicated for your application.

 

[Harleyd315]

If you plan on using the cord to power the shop later on then why not size it for the full output of the generator now, 208-3ph 34 amps i think and around 50 amps 240 single phase if my memory is correct. just my thoughts

 

[Triple Jim]

That could be a very good suggestion, depending on bsorcs' plans for the future. Another thought is that when it's running just the saw, the 003A's breaker is really not going to give much protection. Ideally you'd have a separate 20A breaker to the saw.

 

[steelandcanvas]

2 very good suggestions from Triple Jim and Harleyd315. I came up with and installed this idea: (1) by sizing my power cable (6-4) to my genset output, and (2) using a temporary construction power box which has circuit breakers and GFCI protected receptacles. I mounted an 8x8x4 NEMA 3R enclosure on top of the output lug box on the genset and wired up a CS6364 receptacle in it. I then connect the temp power box and genset together, and select the 120/240 single phase connection. I use this same setup at home (minus the temp power box) and connect to my transfer switch using a CS6364 inlet connector. This design makes my genset (003A) very versatile, I can use the temp power box setup for Club displays, airshows, etc., or plug in for standby power at home.

 

[bsorcs]

Thanks to all for the outstanding guidance...plug/wire specs and 20a breaker...and the slick power box. L14-20s are in hand and 12/4 SJEOOW is on the way. Re power to the shop, the plan is for an Entergy feed and [gulp] one of those pricey Phase Perfect converters. The 12/4 will be for experimenting with the saw and likely connecting from converter to machines in the shop. A 3-phase panel might be installed later, but I do not envision shop work during a hurricane. Already have the 4/4 SEOOW for the house hookup. When I get the saw to fire up I shall re-post.

My Dad would have loved this site!

 

[storeman]

PM sent regarding available 10/5 power cord.
Jerry

 

[bsorcs]

Thinking about breakers. Since the 3-phase motor needs ~6 amps per leg, and because the phases sum to zero, would not a 10 amp breaker suffice. I ask because Jerry has 10 amp breakers!

 

[steelypip]

My rule of thumb is always use the smallest breaker you can get away with. That said, inrush might be 250% of rated current, so you need the thing to not trip on starting during the 25+ amp inrush. If you can get away with 10A, great, but I wouldn't expect to.

 

[bsorcs]

Thanks. I it wasn't for an apparent short-term memory issue, I'd have realized that a 10a, and perhaps a 20a, would not handle the 26-29a inrush I listed in the original post! A 30a breaker seems appropriate.

 

[steelypip]

Well, maybe it would and maybe it wouldn't. It all depends on how that particular breaker is biased for trip speed between surge and continuous current. That's a design property (just as with slow-blow versus fast-blow fuses), and you check out the spec sheet to see just what the surge current numbers are.

It's worth remembering, though, that the purpose of the breaker is to protect everything else in the system by tripping before something else is hurt. A 30A breaker probably would do that as well as a 20A would.

 

[storeman]

Steelypip,
These are Square D QO, type HACR, 3 pole, 10Amp. I suspect they are slow trip speed due to intended HACR use. Given that info, can you help with specs? Like you, I prefer the smallest breaker possible if it will carry the in-rush. Thanks
Jerry

 

[steelypip]

HACR, huh? That's an old breaker - the HACR rating hasn't been required for quite a while. The characteristic curve is on page 20 in this document. As I look at the curve, minimum trip time at 30A should be about 4 seconds. So as long as the start-up surge is a second or so and is <3A, the 10A breaker might work.

Worst case scenario is that it doesn't work and you have to swap the breaker - not that big a deal. It won't hurt anything if it trips during startup.

 

[bsorcs]

I found this Schneider site containing trip curves for the breakers Jerry noted. Based on looking at the graph on p. 19-20, it appears that they are slow-trip breakers, and that the trip time for a 10 amp breaker experiencing an inrush of 3X the rating takes between 3.5 and 16 seconds to trip. A 4X inrush is between 2 and 8 seconds. These times are the same for 1-, 2-, and 3-pole breakers, per the graph legend. These are thermal trips; magnetic trips do not occur until >20X over currents [which the 003 cannot supply]. I guess my questions, based on these numbers, are: 1-if a breaker takes 2 to 8 seconds to trip, and the current is still ramping up during the 2 to 8 seconds, is such a breaker safe to use to start the motor I described in #1; and 2-might such a delay be what the "RLS=40" is intended to deal with?

frame A225; type SC; 855 rpm; 220v, 6.1a; 440v, 3.0a; code = H; and RLS = 40

http://static.schneider-electric.us...rs/QO-QOB Circuit Breakers/0730CT9801R108.pdf


Steelypip is the man...and much quicker on the draw! So, I guess the unknown is the duration of the surge, but it is reassuring to think that this particular 10a would work.

Again, many thanks, folks.

 

[bsorcs]

Wired the saw before Xmas; finally getting back it. I used the box and breaker from Jerry as shown below. I have questions about grounding, so I am requesting yet another consult.

In the box, cord#1 comes in from the genset; #2 goes to the switch; #3 is the return from the switch to #4, the outlet the motor plugs into.
1-Should the ground in cord#1 tie to the bolt at right center instead of to the bar at lower left?
2-If the ground bar is acceptable, can I yank the bare copper wire?
3-Should the ground in cord#3 be tied into #4?
4-I suspect that I need a ground connection to the saw frame?