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#87122 - 01/22/04 05:06 PM Disco Size  
drillman  Offline
Member
Joined: Mar 2003
Posts: 97
Somewhere in Texas
We need to replace an existing electric hot water heater with one the same size.

36 KW, 3 phase 208 volts.
Label states it draws 82 amps.
The breaker in the panel is 125 amps.
Fed with 1/0 copper.
This is what the instructions state.

There is an existing 200 amp disco in the same room as the heater.

Question is can I use a 100 amp disco or would that be a violation?

The problem is that the new water heater is the same KW as the old one but has more capicity and is physically bigger. It intrudes on the working space for the disco and a smaller disco might do the trick. The old water heater also intruded on the working space for the disco but not as much.

I was also thinking of tossing the disco, the panel breaker is actually 5 feet away in the room next door. Would that be "within sight"? It is a different room with its own door but is right next to the hot water heater room. Both are rather small closet sized about 5 X 5 feet.


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#87123 - 01/22/04 05:37 PM Re: Disco Size  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Next room does not sound like it is within site.

However you can get rid of the disconnect all together if the breaker is capable of being locked off.

Quote
422.31(B) Appliances Rated Over 300 Volt-Amperes or 1/8 Horsepower.
For permanently connected appliances rated over 300 volt-amperes or 1/8 hp, the branch-circuit switch or circuit breaker shall be permitted to serve as the disconnecting means where the switch or circuit breaker is within sight from the appliance or is capable of being locked in the open position.


Your 2 amps over being able to use a 100 amp disconnect, unless this heater is larger than 120 gals.

Quote
422.13 Storage-Type Water Heaters.
A branch circuit supplying a fixed storage-type water heater that has a capacity of 450 L (120 gal) or less shall have a rating not less than 125 percent of the nameplate rating of the water heater.


See if you can get a lockout device for the breaker. [Linked Image]

[This message has been edited by iwire (edited 01-22-2004).]


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#87124 - 01/22/04 08:17 PM Re: Disco Size  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
If the subject switch is non-fused, then maybe an 82-amp load on a 100-amp switch is acceptable in its listing.
  • SWITCHES, ENCLOSED (WIAX)      [UL 2003 WHITE]
    Switches without fuse holders (unfused) have been tested to determine their acceptability for continuous operation at their marked rated load.
    Fused enclosed switches are marked, ‘‘Continuous load current not to
    exceed 80 percent of the rating of fuses employed in other than motor circuits.’’





[This message has been edited by Bjarney (edited 01-22-2004).]


#87125 - 01/22/04 10:54 PM Re: Disco Size  
drillman  Offline
Member
Joined: Mar 2003
Posts: 97
Somewhere in Texas
I figured someone would bring up the lockout thing. What I do not understand is do I need a Permanent lockout device installed on the breaker? Such as a frame mounted lockable arm?

I have a lockout kit that has plenty of those plastic lockouts that will fit this breaker.
But I am not sure if this is what the code means.

Get this, the engineer wants the disco moved outside so we get the required clearence. I guess it would work because all discos I have seen that size have pre punched padlockable holes. Of course we would need to buy a new 3R disco.

The engineer sure wants to spend a lot of time and money on a rather simple problem. Plus its his own damn fault, he is the one who speced the water heater as larger than the existing.


#87126 - 01/23/04 06:40 AM Re: Disco Size  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Bjarney That is interesting info.

Not that I really think that 2 amps over is the end of the world but how does that UL listing fit in with the requirement in 422.13?

422.13 is asking for 125% and I see no wording to indicate that can be waved if the equipment is 100% rated.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#87127 - 01/23/04 04:59 PM Re: Disco Size  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
iwire, my guess is that the nonfused disconnect switch is not an overcurrent device and not considered part of the branch circuit, similar to the lesser ratings for nonfused switches permitted for motors, usually for the similar purpose of local isolation.




[This message has been edited by Bjarney (edited 01-23-2004).]


#87128 - 01/24/04 10:55 AM Re: Disco Size  
PCBelarge  Offline
Member
Joined: Jun 2003
Posts: 681
Dobbs Ferry, NY, USA
Drillman
The lockout has to be permanent, a lot of the manufacurers have a part that can be installed to the panel cover, depending on the model number.

Pierre


Pierre Belarge


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