Sierrasparky
Senior Member
- Location
- USA
- Occupation
- Electrician ,contractor
is there any issue using 240 water heater element on 208 service?
240v water heater element on 208
- Thread starter Sierrasparky
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
No code issues, unless the manufacturer's literature specifically states that it is for use only on a 240 volt system. But there is an operational concern. It will operate at 75% efficiency, and will heat water that much slower. The 75% is based on (208/240) squared.
DetroitEE
Senior Member
- Location
- Detroit, MI
It'll take longer to heat the water
that's about the only issue I see.The heating element is a purely resistive load, so it should draw less current than if there were 240V going to it, proportional to the voltage being supplied (so it will be 208/240 times the current).
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
a 4500 watt element rated at 240 volts is really 3380 watts at 208 Volts. But be careful-- 3380/208= 16.15 amps. IMO you can only go 150% which is 24.375 with OCPD. This means a 25 amp is the max OCPD you can use.
Art.422.11(E)
Art.422.11(E)
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
That is how it will perform, but the rating did not change. A transformer (480 volt primary) rated for 150 KVA does not become a 75 KVA-rated transformer, just because you choose to supply it with a 100 amp breaker. A 5 HP motor does not become a 3 HP-rated motor, just because you choose to use it to supply a 3HP mechanical load. A heating element rated for 4500 VA at 240 volts is still rated for 4500 VA, even if you choose to supply it with 208 volts, or unless the manufacturer has given it a separate rating at different voltages.
Didn't we do this dance once already, recently?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yeah we did, and I still think my way is the right way.T
Didn't we do this dance once already, recently?
If the unit stated 208/240 V and 3380/4500 watts would you change your tune?
Sierrasparky
Senior Member
- Location
- USA
- Occupation
- Electrician ,contractor
Thanks for the info.
That doesn't make it less efficient.
Efficiency is generally taken as output power/input power.
In this case both input and output will be reduced as the square of the voltage ratio.
Maybe it will be 75% as effective.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree that this is correct based on what you will get by using the 240 volt heater at 208 volts.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
I would. If the unit only said 4500 watts and that it can operate at 240 volts or 208 volts, would you change your tune?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Nope. Simply because it can't operate at 4500 watts at both voltages.I would. If the unit only said 4500 watts and that it can operate at 240 volts or 208 volts, would you change your tune?
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
But the key word in the code article is "rating," not "OPErating." I am speaking about a circumstance in which the only rating placed on the item is a 4500 VA rating. I would certainly make the same design decision that you are describing, but I submit that the code, as written, does not require me to do so.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I would agree the wording may not be there but you asked would I change my tune and I said Nope.....:grin:
If the unit's nameplate states 240V, and it is id'd on the nameplate as UL, can you operate it at 208V per the NEC?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Technically no....
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
So, every time there's a brown-out or other voltage-reducing event, all of our single-voltage-rated loads become non-compliant.
Yeah we did, and I still think my way is the right way.
Just read the nameplate of an electric water heater
240/208V 1phase
4500/3380W (same for both upper and lower elements, non simultaneous operation)
Name that tune.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Another sign of non-simultaneous operation: "Upper element: 4500 watts, Lower element: 4500 watts, Total: 4500 watts."
- Status