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#90411 11/20/04 01:16 PM
Joined: Feb 2002
Posts: 375
G
George Offline OP
Member
A motor, Delta bandsaw, has a name plate with the following information:

120/240 volts
1.5/2.0 hp
12.8/8.6 amps

For 120 volt use it appears that a 20amp circuit is required.

In reality the motor is

120/240 volts
2.0/2.0 hp
17.2/8.6 amps

Now, a 25amp circuit is required.

What prevents manufacturers of other equipment from "derating" their products to avoid the 80% or 50% rule.

I can see manufacturers selling a suite of kitchen appliances - dishwasher, disposal, refrigerator, and freezer, that all fit on one 20amp circuit.

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#90412 11/20/04 05:37 PM
Joined: Feb 2003
Posts: 169
R
Member
I guess the testing lab listing would be one safe guard. You wouldn't think they would get their listing with improper labeling for the motor.

[This message has been edited by russ m (edited 11-20-2004).]

#90413 11/21/04 01:50 AM
Joined: Jul 2004
Posts: 9,677
Likes: 9
G
Member
From my experience they go the other way and inflate the power of their machines. The real test would be to measure the power used when the machine is loaded to a reasonable maximum load.
My "2HP" table saw will trip a 15a(120v) breaker if I am really loading it down, like ripping 2" hardwood but it never trips a 20. The motor overload will go first.


Greg Fretwell
#90414 11/21/04 07:11 AM
Joined: Sep 2003
Posts: 650
W
Member
And most '5 Hp' vacuum cleaners work fine on a 15A circuit, though the lights may dim a bit [Linked Image]

-Jon

#90415 11/22/04 11:37 PM
Joined: Feb 2002
Posts: 182
B
Bob Offline
Member
George your post
"What prevents manufacturers of other equipment from "derating" their products to avoid the 80% or 50% rule."

What do you mean by the "80% rule"?

#90416 11/23/04 12:36 AM
Joined: May 2003
Posts: 2,876
E
e57 Offline
Member
I think I remember "hearing" about this rule, and never found it anywhere (except for AC units.) But the idea was not to load a circuit past 80%. I think it is an older motor rating rule no longer in use. Which is not the same as sizing the circuit conductors, over-current and short-circuit protection in that application for bandsaw.
Quote
440.62 Branch-Circuit Requirments
(C) Where Lighting Units or Other Appliances Are Also Supplied. The total marked rating of a cord-and-attachment-plug-connected room air conditioner shall not exceed 50 percent of the rating of a branch circuit where lighting outlets, other appliances, or general-use receptacles are also supplied. Where the circuitry is interlocked to prevent simultaneous operation of the room air conditioner and energization of other outlets on the same branch circuit, a cord-and-attachment-plug-connected room air conditioner shall not exceed 80 percent of the branch-circuit rating.


Mark Heller
"Well - I oughta....." -Jackie Gleason
#90417 11/23/04 01:26 AM
Joined: Feb 2002
Posts: 375
G
George Offline OP
Member
e57 has the correct code section.

It seems to me that we trust equipment manufacturers to be honest about the currrent draws so that we can supply appropriate circuits.

This instance of understating the current draw raisses some issues for me. (Especially since I design close to the limits.)

#90418 11/23/04 01:50 AM
Joined: Jul 2004
Posts: 9,677
Likes: 9
G
Member
How about 210.23(A)(1) Cord-and-Plug-Connected Equipment. The rating of any one cord-and-plug-connected utilization equipment shall not exceed 80 percent of the branch-circuit ampere rating.


Greg Fretwell
#90419 11/23/04 06:04 PM
Joined: Jun 2004
Posts: 220
T
Member
80 percent is the inverse proportion of 125percent. so, 80 percent of the rating, or 125 percent of the load should be the same.


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