55 amp double pole Murray or Siemens double pole??

[Raisedonadeere]

I am trying to help son who spends all his money on hunting and stays too broke to fix things right

The resistance heat is powered by a 50 amp double pole Murray breaker through 6ga copper nm-b. The furnace has an internal 60 amp breaker so I assume it should have been powered by a bigger wire and 60 amp breaker. Some jake leg sold and installed this as a surplus’s unit for a very low price to replace a unit that ran off the 50 amp service.

But it ran for a couple of years with an occasional breaker pop my son say once or twice a season. This year it has become more of a nuisance of coming home to a cold house, because heat pump also will be off due to no power to blower or and thermostat.

My question, — my thinking was to install a 55 amp breaker to help this border line situation since the wire is rated at 55 amps. But I cannot find a 55 amp breaker.

The breaker itself could be going bad but if I replace it I would want a 55 amp if such exists in a Siemens or Murray, maybe cutler hammer equivalent.

But last of all would you dare put a 60 amp in there. I can’t believe I said that. Furnace is about 15 feet from main panel and wire is in open air except for about 2 feet exiting panel.

 

[Bert_]

There are no 55a breakers or fuses. Since the wire is rated 55a and that is not a standard breaker size you are allowed to round up to a 60a breaker. As long as the load does not exceed 55a of course.

 

[wyliesdiesels]

Can you post a picture of the nameplate on the heater?

The breaker needs to be listed and labeled for use in that panel.

You didnt say what brand of panel you have but if its a murray then you need a murray.

 

[Raisedonadeere]

Can you post a picture of the nameplate on the heater?

The breaker needs to be listed and labeled for use in that panel.

You didnt say what brand of panel you have but if its a murray then you need a murray.

It’s a Murray and most of the breakers are Murray but Siemens seems to have some identical breakers as I read up on it and indeed there are some Siemens in there. The panel is a Murray 200 amp 40 slot as sold by Lowe’s in 1973. Don’t know if label is still there or not, but next time I will look for it.

But as Burt said as I suspected 55 amp breakers do not exist. I will do a bit more study on the advisability putting a 60 amp breaker on short open air exposed 6ga copper nm-b.

 

[sberry]

Like the man said,,, a pic of the name plate would help but no one ever burned the place down with a 60 on a 6. I am not sure how long it would have to run on 8 to start a fire?

 

[Dagny]

Pull the breaker out and look at the buss bar they are known to corrode and burn.

 

[wyliesdiesels]

It’s a Murray and most of the breakers are Murray but Siemens seems to have some identical breakers as I read up on it and indeed there are some Siemens in there. The panel is a Murray 200 amp 40 slot as sold by Lowe’s in 1973. Don’t know if label is still there or not, but next time I will look for it.

But as Burt said as I suspected 55 amp breakers do not exist. I will do a bit more study on the advisability putting a 60 amp breaker on short open air exposed 6ga copper nm-b.

siemens owns murray but I dont think that happened until way after 1973. technically theyre not interchangeable since murray is MP and Siemens is QP.

Here is a discussion about it on mike holt forums

https://forums.mikeholt.com/showthread.php?t=97395

You need to know what the load of the heater is. Post the nameplate or the wattage. since its considered a continuous load, the wire would need to be rated for 125% of nameplate.

 

[Raisedonadeere]

need to know what the load of the heater is. Post the nameplate or the wattage. since its considered a continuous load, the wire would need to be rated for 125% of nameplate.

Yea that continuous load thing is what gave me pause. I am still guessing the thing has been running right on the border of 50 amps. I am goung to see if I can power the motor and thermostat off a separate circuit that was used for that purpose on the old install. That would reduce the draw on the heater power by a few amps.

And yes Dagny this panel did have a burnt buss bar connection on another circuit a few years ago. We sanded it and swapped in a lower amp circuit using some dialectic grease. It still looks good. Didn’t check this breaker yet. But it felt cool. The one that failed was actually getting hot. That is how I caught it. Upon investigation found the burnt bus connection.

 

[Bert_]

I am goung to see if I can power the motor and thermostat off a separate circuit that was used for that purpose on the old install. That would reduce the draw on the heater power by a few amps.

90% chance this install is correct except the 50A breaker should be a 60A. Post the nameplate info for the heater and we can tell you.

60A breaker in the unit sounds like a 10KW heater. 10KW is about 41 amps plus a couple for the fan. So say 44A total X 1.25 = 55A minimum circuit ampacity. You can use #6 NM with a 60A breaker. This is 100% legal and correct, larger wire would be a waste of money.

 

[TRWham]

Depending on how the heat coil(s) are wired, you might be able to drop some of the load by rewiring if it concerns you. Also, I believe Eaton does make classified breakers that are UL listed for use in place of Murray MP breakers.

 

[reader2580]

siemens owns murray but I dont think that happened until way after 1973. technically theyre not interchangeable since murray is MP and Siemens is QP.

Current MP and QP breakers look to be identical in every way. Siemens has chosen not to UL list them as interchangeable so code prohibits interchanging them.

Folks have dismantled them both and find them they are identical internally.

 

[Raisedonadeere]

Current MP and QP breakers look to be identical in every way. Siemens has chosen not to UL list them as interchangeable so code prohibits interchanging them.

Folks have dismantled them both and find them they are identical internally.

I have installed Siemens in several situations where I needed to help folks with a circuit addition project, - pools, hot tubs, hvac, RV etc. None of these situations resulted in compromised performance. At the time I didn’t know about the technicality of code requiring use of listed only breakers. I found what fit and looked at the tripping specs to deal with inductive loads.

 

[Aceman]

12 posts and no name plate info yet. Why?

Electricians size and in this case, troubleshoot circuits based on name plate info.

 

[reader2580]

I have installed Siemens in several situations where I needed to help folks with a circuit addition project, - pools, hot tubs, hvac, RV etc. None of these situations resulted in compromised performance. At the time I didn’t know about the technicality of code requiring use of listed only breakers. I found what fit and looked at the tripping specs to deal with inductive loads.

The breakers are identical other than the brand name and model number. Electrically you did nothing wrong. Performance wise you should have no issue since folks have found them to be identical internally.

Siemens chooses not to UL list them for use in a Murray panel and vice versa. It is a technical violation of the NEC and some inspectors would ding you for it. For some reason Siemens doesn't want Murray and Siemens interchanged.

I was using some Murray breakers in my load center until I found it was against code. At $4 each for replacements it wasn't a big deal to replace a few breakers.

 

[wyliesdiesels]

12 posts and no name plate info yet. Why?

Electricians size and in this case, troubleshoot circuits based on name plate info.

Yeah i asked for it right up front in post #3.

 

[Raisedonadeere]

Yeah i asked for it right up front in post #3.

I was not intending to be asking for help on diagnosing my furnace. I was just curious on where the boundaries are in a situation since a wire is rated 55 amp and I am tripping a 50 amp breaker occasionally. I know the load is near 50 amps. Some combination of events during defrost with heaters kicking on or power line fluctuations which happens in this rural area.

One of these days I will figure out how to upload pictures.

 

[Bert_]

I was not intending to be asking for help on diagnosing my furnace. I was just curious on where the boundaries are in a situation since a wire is rated 55 amp and I am tripping a 50 amp breaker occasionally. I know the load is near 50 amps. Some combination of events during defrost with heaters kicking on or power line fluctuations which happens in this rural area.

One of these days I will figure out how to upload pictures.

Your missing the whole point. The wire might be the right size, but we can't help if you won't give us crucial information

 

[Jim greengo]

I can still get Murray breakers In Omaha if you cant find them where you are,let meknow and I'll get you the number for Omaha supplier.

 

[Raisedonadeere]

The furnace has its own internal 60 amp breaker, looks almost identical to a square D breaker. so I am not concerned with protecting the furnace. Just want to get all that is available from the wiring. And it has been running for several years with occasional main panel 50 amp breaker pop. It could turn out that something in the furnace is intermittently shorting. But rarely will it do it while we are watching. When it trips we turn it back on usually runs for several days, but once or twice it immediately tripped again. I will track down the electrical glitch if necessary but for now it looks like borderline breaker size. I could not find a lable but it is a carrier unit.

 

[Bert_]

The furnace has its own internal 60 amp breaker, looks almost identical to a square D breaker. so I am not concerned with protecting the furnace. Just want to get all that is available from the wiring. And it has been running for several years with occasional main panel 50 amp breaker pop. It could turn out that something in the furnace is intermittently shorting. But rarely will it do it while we are watching. When it trips we turn it back on usually runs for several days, but once or twice it immediately tripped again. I will track down the electrical glitch if necessary but for now it looks like borderline breaker size. I could not find a lable but it is a carrier unit.

Again the #6 might be correct. But no one can say for sure without more information.

Say it's a 10kw furnace #6 is correct.

But maybe it's 11.5kw now it needs #4.

Both scenario's will need a 60A breaker.

 

[wyliesdiesels]

The furnace has its own internal 60 amp breaker, looks almost identical to a square D breaker. so I am not concerned with protecting the furnace. Just want to get all that is available from the wiring.And it has been running for several years with occasional main panel 50 amp breaker pop. It could turn out that something in the furnace is intermittently shorting. But rarely will it do it while we are watching. When it trips we turn it back on usually runs for several days, but once or twice it immediately tripped again. I will track down the electrical glitch if necessary but for now it looks like borderline breaker size. I could not find a lable but it is a carrier unit.

Without the critical info listed on the nameplate, there is no way to know if the wiring is correct size.

You dont have to post a pic. You could just list the nameplate ratings.

 

[Raisedonadeere]

Again the #6 might be correct. But no one can say for sure without more information.

Say it's a 10kw furnace #6 is correct.

But maybe it's 11.5kw now it needs #4.

Both scenario's will need a 60A breaker.

Thanks for that info. I am going to chase down the furnace specs tomorrow. I hope it is just a 60 amp breaker deal.