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02-12-2013, 01:14 AM #1
main breaker and unit breaker/switch questions
went to a mobile home and found the following;
80 amp main panel breaker feeding 2 60 amp unit switches(breakers).
Electric strip heat- 4 elements and blower, so 85+ with all on.
wire comes into unit's bottom switch and then jumper wires feed the upper 60 amp switch.
1) bottom unit switch is overheating and tripping, why? I questioned if the total amp draw was going through that switch since the feed came into the back/incoming side and then split off. Sparky said no.
2) is the jumper set up okay? usually there is a buss bar or factory metal and plastic splitter to do this.
sent our sparky out there and he determined the wire size could only support 80 amp load.
I had left 4th element disconnected, so only 65+ amps on the 80 amp panel breaker. unit's top switch had 2 elements and fan, bottom now has only 1 element.
02-12-2013, 06:53 AM #2
First, when you say "main," you mean the branch circuit breaker, The Main is controlling the power to the panelboard inside the cabinet at the service entrance.
To get this right:
1) determine the unit label FLA with all elements energized.
2) heating is a continuous load (424.3 (B), 2008) so the conductors and overcurrent devices are sized at 125% minimum of the FLA value you just found.
3) check the equipment label to see if this unit requires 60° C conductors.
You can post back here with the values you found, and we can go from there. From what you have posted, the conductors and branch circuit overcurrent protection may not be properly sized for this installation. This is not uncommon.
Note that Article 424 requires a separate disconnecting means to be within sight of the heater in cases where there is a supplementary overcurrent device(s) as this heater does (424.19) .
Go through the entire article and see what applies.
As for the tripping, take an IR temp reading of the breaker, and see if it is getting too hot. Sometimes, the fault is heating from a bad connection to the breaker, and sometimes, it is the breaker itself. In either case, that breaker must be replaced, if it has been heated to a higher than normal operating temp.
02-12-2013, 04:53 PM #3
Thanks for the stuff to read, I will go through it.
I will not be going back, as I am not a license sparky.
I really wanted to know if the wire jumper set up was proper or if it should be the OEM fabricated type since this is a single branch feed to the 2 unit switches?
Yes, I did mean the branch feed to the unit was an 80 amp. Spark said it was 3 gauge aluminium wire.
With some wiggle, it would be 89 amps total. 21 on each of 4 elements and 5 on the blower motor.
02-12-2013, 06:23 PM #4
89 amps total x 1.25 = 111.25 amps selection current for the breaker and conductors.
If using Al conductors and it the terminations are 75C, then the required conductors would be 1/0, and the branch circuit ground fault, short circuit, and overcurrent protection would be 125 amps.
The question of the jumper has to do with the UL listing, since it is inside the unit. It would have to be using the same connectors, material, and size as the OE to maintain the UL listing.
Whoever goes back there MUST upgrade the wiring and overcurrent device for this unit. Also note the requirement that the disconnect be WITHIN SIGHT of the unit.
Let us know if your electrician makes the correct repairs.......
02-12-2013, 10:32 PM #5
my understanding is that he left the unit as I did, operating on only 3 elements and the fan.
he replaced the 80 amp branch circuit breaker with same because it would not reset when he turned it off.
no wiring was replaced.
by the calculation, (21x3)+5)x1.25=85 amps, so breaker is still too small.
as for the overcurrent device, do you mean the 80amp breaker in the main panel or does this refer to the 2 60amps in the unit?
02-12-2013, 11:15 PM #6
1 lug, 1 conductor.
The over heating problem you are getting with the bottom breaker likely has its roots in having 2 conductors stuffed in the lugs of the breaker.
Every equipment manufacturer I've ever checked has some sort of single point power entry kit.
Usually it includes a jumper bar assembly that connects between the breakers, possibly a sticker to amend the units wiring diagram, sometimes extra sheet metal bits, a larger ground lug, etc..
Some, like Goodman, have a terminal block that the supply wires connect to one side of, and 4 wires from the block to the breakers.
Most of the breaker manufacturers have some sort of jumper bar available, with appropriate UL listings, etc., for sets of 2 or 3 breakers to be fed by a single power supply.
Note that if both breakers don't have the same size lugs, you can't use a jumper bar. Goodman sent out bulletins about the issue regarding their 15kw heat packages a few years ago, which is why their single point kit is a terminal block and wires.
If more government is the answer, then it's a really stupid question.
02-13-2013, 07:13 AM #7
What a difference the correct installation makes!!!
02-13-2013, 07:28 AM #8
Okay, so I can see that your calculation included the 125% factor for the continuous load.
75C AL #1 wire is good for 100 amps, so you have the continuous load of 85 amp selection current covered.
A 90 amp breaker is needed, (next size up).
AND the unit must have the correct power distribution parts, as shown above, AND the unit disconnect MUST be within sight of the unit. This is NOT the breakers in the unit.
02-13-2013, 07:45 AM #9
A couple of additional notes:
1) the FLA to be used is supposed to be printed on the equip label, OR
2) the label will give you:
a) a MCA, or minimum circuit ampacity, which should be their calculation for the continuous load value, and that is your selection current using the Table in article 300, and
b) an MOD, or maximum overcurrent device to be used with the MCA, and that would be your 90 amp breaker, and
c) IF the unit label specifies FUSES alone, then fuses must be used. More often these days, you see equipment that says "fuses/breakers." So, breakers are then okay.
02-13-2013, 09:19 PM #10
02-13-2013, 09:19 PM #11
02-14-2013, 11:00 AM #12
02-14-2013, 12:26 PM #13
Now that is nice and clean.Certified parts changer.