Heat pump fuse blow out

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Old 01-07-15, 11:51 AM
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Question Heat pump fuse blow out

My home has an heat pump, which has 60A cartridge fuse. It worked fine for five years we live there till we added an addition to the house. We added second heat pump for the addition with new wires from the electrical panel, the second heat pump has its own 40A cartridge fuse. Then fuses from both heat pump started to blow out, about once a month (only in winter). It is so weird since nothing change from the first heat pump. Could you think anything I should check? Thanks.
 
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Old 01-07-15, 12:03 PM
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Welcome to the forums.

You are blowing fuses on both heatpump systems ?
 
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Old 01-08-15, 04:50 AM
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Only one heat pump fuse burned each time, no pattern found.
 
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Old 01-08-15, 08:22 AM
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Is there any Aux heat coming on when the fuses blow? Do they blow at the same time?
Geo
 
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Old 01-08-15, 08:49 AM
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I am not sure if Aux heat is on when the fuses blow, I would say most likely since I feel the blow up happened when the outside is very old, but I am sure it wouldn't blow fuse every time Aux heat on. Each time only one fuse blow, either 40a or 60A, not pattern found. I'd like to emphases, 60A never blows out before we installed new heat pump. Thanks for your time and knowledge.
 
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Old 01-08-15, 09:07 AM
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My point is you are having problems with TWO separate systems. Only one fuse blows at a time in a system is because they're 240v circuits.

I feel the blow up happened when the outside is very old,
If your wiring is old is should be checked by an electrician. Technically, both systems should be measured with an amperage probe to see if they are overloaded.
 
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Old 01-08-15, 09:33 AM
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It could be that in cold weather the overall demand - not only at your house, but in the neighborhood is such that the line voltage drops , for example from 240 to 210 - a sort of brownout. Then when the compressor starts, the starting current surge could be prolonged - and there goes a fuse. Do you notice the lights dim momentarily when the compressor starts ?

Have you measured your line voltage (preferably measured at the fuse box or as close as is convenient) ? Does it change much in periods of high and low demand ?

I don't know if slow blow cartridge fuses are available now - but that might be worth a try.

Also, are you replacing the cartridge fuses with fresh (not ones that having been sitting in the basement for ten years) ? The fuses do deteriorate - I used to have problems with cartridge fuses failing from old age (hard to believe, I know). That problem disappeared with conversion to circuit breakers instead of fuses.

An interesting problem - take a minute to post the resolution when you figure it out :-)
 
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Old 01-08-15, 10:34 AM
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Good thought on the fuses, what type of fuse? OT or TD. Are these units supplied from a circuit panel?Who is the mfg.and what are the model #'s of the units?any wiring Dia's you can post?
Geo
 
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Old 01-08-15, 01:07 PM
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Most time, I use one time fuses, but I did try time delayed fuse once and it still burned. I will try TD fuse again.
Old unit, three breakers in the electrical panel, marked as AC (50A), Furnace I (60A) Furnace II (60A). Two thick cables from the panel to two fuse boxes (I and II, both 60A), then go to furnace unit (Carrier FK4DNF005).
New unit, two breakers in the panel, marked as AC (30A), Furnace (60A). One thick cable from the panel to the 3rd fuse box (40A), then go to furnace unit (Trane 4TWB32024C1000AA).
Two fuses in each fuse box, each time, only one fuse got blowed. I don't recall any fuse burned in fuse box I, all of them from fuse box II and III if I recall correctly.

Thanks again for your help
 
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Old 01-08-15, 03:37 PM
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So it appears you have 2 furnaces for the old unit,and one heat pump condenser outside.
New unit has 1 furnace and 1heat pump condenser outside.
Maybe some pic's would help clarify this, at least the inside.
It seems like the fuses that are blowing are related to the electric heat in which case the OT fuse are fine.
Geo
 
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Old 01-09-15, 06:28 AM
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I believe you are right about the furnaces and condensers. One question, if I change cartridge fuses 5A larger and make breakers have values as original cartridge fuses, would it make breakers to jump instead of burning fuses? Thanks.
 
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Old 01-09-15, 08:40 AM
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I wouldn't do that, one other question ,do these 2 fuses blow at the same time?
Geo
 
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Old 01-12-15, 05:56 AM
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each time only one fuse blow, either from fuse box 2 (old unit furnace) or box 3(new unit furnace). each fuse box has two fuses, only one of them blow.
 
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Old 01-12-15, 09:15 AM
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WOW!do the condensers continue to run when these fuses blow?can you post some pics of the switches where these fuses are located?
Geo
 
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Old 01-13-15, 11:02 AM
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No, once a fuse blows, that fuse connected condenser and furnace blower stopped running, even the thermostat is black (no battery, powered by wires from the furnace). I found some pictures from internet which are same as my fuse box. I have three of those fuse boxes, they are nailed on wood board. Each fuse box has two fuses, only one of them blows. [ATTACH=CONFIG]44871[/ATTACH][ATTACH=CONFIG]44872[/ATTACH]
 
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Old 01-13-15, 01:50 PM
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Is there any kind of connection between the boxes?that's why I was asking for pics of your setup,not sure if the question was asked,but are both systems running at the same time when this happens ?
Geo
 
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Old 01-14-15, 08:53 AM
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there are not connection between boxes except the wood board:-) I did trace all wires from fuse boxes to same electrical panel, but looks normal as far as I can see. I will try to upload more pictures once I get home. I am not sure if both units are running when fuse blow, but I think if that's the case, it should blow much often. thanks.

Richard
 
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Old 01-14-15, 02:51 PM
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Have you checked the supply voltage as a previous post has suggested and also do you notice your lights dim at any time before the fuse blows,any issues with other appliances ie. electric range,dryer?You could call the POCO and explain what's going on and have them check their supply voltage,and meter connection.
Geo
 
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