Silly me. I always thought that higher voltages meant lower amperage. You know... like transmission lines use 7200v and up so the amperage is much lower.
I guess I should rewire my house for 5 volts so I can use tinsel wire.
Engineer Wants (3) 208V 20A Hand Dryers on 30A Circuit
- Thread starter Willoferd
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Silly me. I always thought that higher voltages meant lower amperage. You know... like transmission lines use 7200v and up so the amperage is much lower.
I guess I should rewire my house for 5 volts so I can use tinsel wire.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
That's true when the equipment is built to natch the voltage. When talking about delivering a given power, the P = E x I math applies. To deliver a given power, current varies inversely with voltage. Also, loads like motors use less current when the voltage increases (within its design voltage range).
When talking about applying a different voltage to equipment with no change to the equipment, then the I = E / R Ohm's Law math applies. The current varies proportionately with applied voltage. This describes most electrical loads which behave as resistive loads do. If the voltage increases, so does the current.
If you apply only 5v to loads designed for 120v, so little current would result that you probably could. 120 / 5= 24, so 1/24 as much current would flow at 5v compared to 120v.
On the other hand, if you want the same amount of power on 5v as you would on 120v, you'd have to be able to supply 24 times as much current, so you'd need very heavy wire.
Look at your car wiring. Battery and spark-plug cables are about the same diameter, but battery cables are mostly conductor, while spark-plug cables are mostly insulation.
Electricity is transmitted at high voltages over distances because insulation is cheaper than conductor, and more importantly, voltage drop is dependent on current, not voltage.
By the way, 7200v is relatively low for even primary distribution. Transmission voltages are in the 100Kv and up range; some long-distance lines are into the megavolt range.
kwired
Electron manager
- Location
- NE Nebraska
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- EC
Other than different voltages looks like they basically only have one model to choose from, wattage of the different volt units are about same anyway.
I have not installed all that many hand dryers so don't know what is common.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
If a different unit with different resistance to get same output watts then higher volts will be less current.
If same unit has lower voltage applied but resistance remains constant, then current drops, but so does wattage.
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
I would like t know what the MFG recommends for branch circuit protection. It may not be allowed on a 30. I would think this would be a non continuous load so I don't see why you couldn't put 3 on a 20A
Malywr
Senior Member
- Location
- New Jersey USA
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree, protecting a 5.6 amp appliance at 30 amps could be problematic unless specifically allowed by the manufacturer. Does the NEC permit a 5.6 amp appliance on a 20 amp circuit? If so install all three on a 20 amp circuit and you're code compliant unless the manufacturer or the NEC limits the appliance to a 15 amp circuit or requires an individual branch circuit for each unit.
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
I looked on there web site only because there made in my Town (East Longmeadow, Ma). They give voltage, amps, wattage with and without motor for different voltages no other info on branch circ. etc
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
The rule is 422.11.
A. says if protective device is marked on the appliance then that is what it will be.
B and C don't apply to this particular appliance
D possibly could apply - and has a max of 50 amps (edit) read it again, should not apply because this has no surface heating elements
E - depends if you call this a motor operated appliance - it has a blower motor but the major load is the heating element. If E does apply then max overcurrent is 20 amps for a 13.3 amp or less rated appliance or 150% for all others.
F doesn't apply and G involves motor overload protection for motor operated appliances.
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