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Old 03-07-2016, 01:04 PM   #1
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Default Disconnect Switch Noob Question!

Hi guys,

While buying a disconnect switch today for a 240vac system i saw on the specification that the max amp is like 20 while the same switch on 600vac is 60amp and was wondering why ? isn't like the total watt that matter only ?

My product was a Eaton disconnect Heavy-duty non fusible 3 poles amp rated 60amps
DH362UGK

Thanks
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Old 03-07-2016, 01:13 PM   #2
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You're sure your spec doesn't call for a minimum of 20 amp? That's a normal, everyday disconnect switch. You're good to go. Disconnect switches aren't rated in watts.

If your spec is for a fused disconnect I could understand a maximum of 20 amps.
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Old 03-07-2016, 01:58 PM   #3
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actualy the rating was for Max Horsepower for every volts, but still im trying to understand.

DH362UGK
Amp Rating: 60 amps

Max HP 3 phases
240vac = 20amps
480vac= 40amps
600vac= 60amps


Why at 240vac 3 phase this disconnect is limited to 20amps while on 600vac it can take 60amps ??



My unit is running on 208vac 20amp and was thinking of buying a normal one 30 amp rated but this part about the Horsepower and voltage confuse me.

Last edited by martindag; 03-07-2016 at 02:02 PM.
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Old 03-07-2016, 02:31 PM   #4
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Quote:
Originally Posted by martindag View Post
...

DH362UGK
Amp Rating: 60 amps

Max HP 3 phases
240vac = 20amps
480vac= 40amps
600vac= 60amps
You are reading this wrong. Look at the top of that column, those numbers are for the HP rating, not the amp rating.

Max HP 3 phases
240vac = 20HP
480vac= 40HP
600vac= 60HP

(BTW, my catalog shows the max HP at 480V as 50HP, not 40)
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Old 03-07-2016, 02:37 PM   #5
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ohhhh ok i get it now! , my bad i thought this was amp, thanks !

so to resume is the disconnect is rated 600vac 60amp MAX

no matter which voltage AC or Amp as long has it under the max rating it's fine (i saw DC is a little different)

and the HP is something else.

Last edited by martindag; 03-07-2016 at 02:41 PM.
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Old 03-07-2016, 02:44 PM   #6
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Quote:
Originally Posted by martindag View Post
...


Why at 240vac 3 phase this disconnect is limited to 20HP while on 600vac it can take 60HP ??
FIFY

Voltage goes down, current for the same HP goes up.
20HP @ 230V = 54 FLA
40HP @460V = 52 FLA
50HP @ 460V = 65 FLA
60HP at 575V = 62 FLA

Now how they can get away with a 60A switch being OK for running a motor with an FLA over 60A, or even AT 60A, I have no idea. The NEC clearly says a disconnect must be rated for 115% of the motor FLA.

But this is a NON-FUSED switch, meaning you cannot use it in a circuit that does not have another OCPD up stream. So maybe they are thinking they can use a "fudge factor" on their FLC rating because something else in the circuit will have to deal with overloads. So if they tested it with UL for 50HP @ 460V and it passes, then it's legit.

If you look at the fusible version of the same switch, the HP listings are lower by one size.


Quote:
My unit is running on 208vac 20amp and was thinking of buying a normal one 30 amp rated but this part about the Horsepower and voltage confuse me.
That's something you would have to ask them. Their data sheet doesn't mention 208V. 20HP @ 208V is 59.5A FLA so if you ask me, they ALREADY took that leap in listing it for motor FLAs over 60A, ergo I would think that the 20HP 208V would be fine. But an AHJ may want to see it in writing.
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Old 03-07-2016, 03:20 PM   #7
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Thanks alot very informative !
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Old 03-07-2016, 04:14 PM   #8
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Quote:
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Thanks alot very informative !
You should see how big his head is to hold all that brain power. This is one wise individual.

We are lucky to have him as a member
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Old 03-07-2016, 06:35 PM   #9
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Almost everything I know I attained by making mistakes...

My favorite saying:
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