Electric Heat - Name plate doesn't make sense

[olly]

Hi Guys,

I am wiring an electric furnace. I have never wired one before. It takes 2 - 2 pole breakers. for the L1/L2 I assume minimum amps is 35.6/39.4 for the 60A breaker and a max of 52.1/56.9. It doesn't say min and max, just min ampacity, which I find confusing.
How do these work, does the circuit board change the amperage based on demand? I am assuming the thermostat will determine how many amps to send to the resistive electrical element, like a high medium or low. Low being 35.6/39.4 and high being 52.1/56.9. Is that correct? Also, L3/L4 is that a second stage? So it only comes on when it needs it?

 

[LarryFine]

L1-2 MCA is 52.1/56.9 depending on voltage, MOC is 60a
L3-4 MCA is 22.3/24.6 depending on voltage, MOC is 25a

This sounds like a 10kw/5kw furnace, probably dual stage.

L1-2 slightly higher than twice L3-4 for the blower motor.

 

[infinity]

If you notice it listed two voltages. For L1-L2 at 208 the current is 35.6, @230 it's 39.4. (When you increase the voltage you increase the current). That is the current draw based on which voltage you're using. The MCA is the minimum circuit ampacity and that number is used to size the conductors. For L1-L2 depending on the wiring method you may need a larger conductor size for 230 volts.

 

[Dennis Alwon]

On L1/L2 Heater they show the amps but the minimum circuit is the amps times 1.25. The moto load is in there also

On L3/L4 it has just the heater amps times 1.25

Obviously 2 circuits are needed for this heater

 

[suemarkp]

These heaters are usually staged, depending on the thermostat control available. It could stage heater on L1/L2 (low), L1/L2 + L3/L4 (high), or L1/L2 (low), L3/L4 (medium), L1/L2+L3/L4 (high).

Also note this is yet another furnace where the manufacturer hosed those who wire in romex. #6 NM cable is good for 55A, but the minimum ampacity required for L1/L2 is 56.9. They could have used a slightly smaller heater or fan motor. But with this ampacity, they are driving you to a 75C wiring method or you jump up to #4 cu in NM cable.

 

[david]

Hi Guys,

I am wiring an electric furnace. I have never wired one before. It takes 2 - 2 pole breakers. for the L1/L2 I assume minimum amps is 35.6/39.4 for the 60A breaker and a max of 52.1/56.9. It doesn't say min and max, just min ampacity, which I find confusing.
How do these work, does the circuit board change the amperage based on demand? I am assuming the thermostat will determine how many amps to send to the resistive electrical element, like a high medium or low. Low being 35.6/39.4 and high being 52.1/56.9. Is that correct? Also, L3/L4 is that a second stage? So it only comes on when it needs it?

View attachment 2572809

Where did you get this sticker from, it looks yellowed and looks like it was never peeled.
The manufacture dosnt know if your going to use the single supply or the duel supply method.

Also the manufacture dosnt know what heater pagage you are going to use.
If you have more than one sticker you have to make sure it's the right one for the heater package that was installed in the furnace.

There is usually additional instructions where these stickers are affixed to the furnace such as copper only.

If no sticker was affixed to the furnace you may see information for a single supply.

There will be a list of heater packages and the correct one would be checked off by the installer

Also note some manufactures send these furnaces out with two 60 amp breakers as the local disconnect.
If that is the case the electrician needs to use the correct breaker size in the panel ahead of the supply conductors or the correct breaker in your case for line 3/4.

A 25 amp breaker is is less common than a 30 amp

On long runs I seen hvac contractors use alum than add a disconnect close to the furnace and supply the furnace with copper from the local disconnect

 

[Eddie702]

This heater need 2 208 0r 230 volt single phase circuits. You can't use 1 circuit it is not listed for that

Circuit L1 & L2 draws 35.6 amps on 208 volt or 39.4 amps on 230 volt. The minimum circuit amps for wire size is 52.1 or 56.9 depending on voltage. The max circuit breaker is 60 amps regardless of voltage

Circuit L3 &L4 draws 17.8 or 19.7 depending on voltage. The minimum circuit amps is 22.3 or 24.6 depending on voltage and a 25 amp breaker is required for either voltage

 

[david]

This heater need 2 208 0r 230 volt single phase circuits. You can't use 1 circuit it is not listed for that

Circuit L1 & L2 draws 35.6 amps on 208 volt or 39.4 amps on 230 volt. The minimum circuit amps for wire size is 52.1 or 56.9 depending on voltage. The max circuit breaker is 60 amps regardless of voltage

Circuit L3 &L4 draws 17.8 or 19.7 depending on voltage. The minimum circuit amps is 22.3 or 24.6 depending on voltage and a 25 amp breaker is required for either voltage

That's true but I have seen very few electric furnaces
Not having a data plate with a single supply option

 

[kwired]

That's true but I have seen very few electric furnaces
Not having a data plate with a single supply option

must be a regional kind of thing? Majority of them I've seen for past 20-30 years were usually intended to have multiple supply circuits (if over ~10kW).

Used to be certain brands were commonly sent out with a common feed kit though you could remove that and supply it with two circuits.

Many lately is a situation of purchasing heat kit separately and installing it in an air handler. You may have nameplate with multiple sections on it and you select which one applies depending on which heat kit you installed, or the heat kit comes with a label you are supposed to place over the original air handler label.

 

[Dennis Alwon]

That's true but I have seen very few electric furnaces
Not having a data plate with a single supply option

Once you have more than 60 amps for electric heat then the load mus be subdivided. It is either done by having 2 circuits or the heater itself will have 2 sets of oovercurrent protective device built in. I have seen it both ways

424.22 Overcurrent Protection.

(B) Resistance Elements.
Resistance-type heating elements in electric space-heating equipment shall be protected at not more than 60 amperes. Equipment rated more than 48 amperes and employing such elements shall have the heating elements subdivided, and each subdivided load shall not exceed 48 amperes. Where a subdivided load is less than 48 amperes, the rating of the supplementary overcurrent protective device shall comply with 424.4(B). A boiler employing resistance-type immersion heating elements contained in an ASME-rated and stamped vessel shall be permitted to comply with 424.72(A).