Expert: Master Bob - 7/23/2004

Question
Hi Bob,
I'm replacing my electric dryer with a gas one.  I plan to use
that 30amp 250v circuit for a 3hp 220v single phase
15amp table saw.  I'm a little confused because it looks like
the table saw doens't need a nuetral.  I was under the
impression it needed 2 hot wires, but he plug has only 3
prongs.  Any ideas?
thanks, Matt

Answer
Hi Matt,

  Sorry just responding...have been straight out against the wall the past few days...

 Based on your description...I do NOT recommend you use the former dryer circuit for this table saw...without making some significant modifications.

 First ....you will need to change the receptacle to match the saw's plug configuration...your dryer more then likely has  a 14-30R (4 prong 30 amp 240 volt receptacle)...and your saw perhaps a 6-16P ( 3 prong 15 amp 240 volt plug)...or something similiar.  For more on these NEMA plug and receptacle Codes, see:
http://www.leviton.com/sections/techsupp/nema.htm

 Secondly....the 30 amp double pole breaker that used to feed the dryer MUST be changed to a double pole 15 amp breaker.....and you will also find the # 8 gauge wire too large to fit either the new breaker or the new saw receptacle you install.... # 12 gauge will be all you need for this saw.

 If you attempt to modify or otherwise run this saw on the current set-up you have...the 30 amp breaker is sized too large...and will not trip in the event of a problem or overload from the 15 amp rated saw...and serious motor damage can (and will) result.

 This table saw is more then likely what we refer to as requiring "straight" 240 volts...with no neutral. It will have only the 2 hot legs and a ground. A dryer on the other hand...requires the 2 hot legs, 1 neutral and 1 ground...especially under the new Codes now in effect. (older dryers in some older homes are grand-fathered and the old 3 prong dryer cords and receptacles can still be used. In new construction...a 4 prong is now minimum.) Most (if not all) dryers and stoves require the neutral so that certain internal circuits will have 120 volts available to operate timers,clocks, etc....the 240 volts being need for the heater elements only. Your table saw does not need this neutral...240 volts straight power is all it needs.

 So....to use this table saw...you will need to make the above modifications (basically start from scratch) for proper and safe operation of this table saw.

Hope this helps...if you need more details, please follow-up.


Best Wishes,

Bob Osgood
Master Electrician


RKO ELECTRIC

www.rkoelectric.com