# Compressor blows fuses



## 99cents (Aug 20, 2012)

Part number of the fuses would help.


----------



## JRaef (Mar 23, 2009)

Assuming you have the correct fuses (per 99cents' question), most likely it's because on really hot days, the utility can't keep up with demand and the voltage drops, which affects the starting current of the compressor and the fuses blow. Not a lot that you can do about the utility, but you could add a soft start to the compressor (assuming it does not have one already). That will reduce the demand on the utility when it starts so that the starting current of the compressor doesn't make a bad situation worse, which helps to keep the fuses from blowing.


----------



## Bad Electrician (May 20, 2014)

Yes and more than likely it is a thermal condition, Have you IR's or performed a FOP test?


----------



## GatewaySparky (Jul 23, 2010)

Bad Electrician said:


> Yes and more than likely it is a thermal condition, Have you IR's or performed a FOP test?


I just did a PIR test this past morning. Conductors on the load side are pretty cool at 93 -115 degrees F. The conduit on the load side is about 20 degrees above room temperature and steady. It is a grounded B phase system, by the way. The manager says that only one fuse seem to blow, the farthest to the right in the disconnect. Disconnect is an older Square D H324N with 200 amp FRN fuses. They are replacing them with the same fuses they have always had for the past 9 years.
I actually got to observe it under load during the workday. I can only obtain a maximum reading of 130 amperes on all phases. The motor is ratedfor 125 amps at 250 volts and 62 at 480 volts The thermometer shows 115 degrees F on phases A and B. The curious thing is the C fuse. The blade on the line side of this fuse reads 212 degrees and I can only assume it will rise. the guys in the shop say the disconnect is very hot to the touch. enough that you can't touch it for very long especially after running all day. Could this make the fuse pop? the guys in the shop are skeptical of such a simple explanation since the fuse is still hard to pull out.
A FOP test? Not sure if I'm capable of doing one. It seems long and complicated and the owner wouldn't be too please if it turned out no results. Maybe a Data logger would help with clues? Thanks to you all for your insight.


----------



## Bad Electrician (May 20, 2014)

Perform an FOP test and then I bet you will replace the Fused Safety Switch


----------



## varmit (Apr 19, 2009)

If the running current is close to the same on all phases and one fuse holder/ disconnect pole is more than a few degrees (7-8%) hotter than the others, replacing the disconnect is a good idea. Jreaf's comment is true also.

Be sure to check the current at the line and load sides of the disconnect and all other connections. Also, meg the motor windings. Nine years is a good long life for an air compressor motor and there could be some insulation breakdown. Being a corner grounded system should have no effect on the problem. Do you know if the fuses only blow on start-up? If so, there could be a mechanical problem with the compressor. As we know, intermittent problems are never easy to diagnose.


----------



## 99cents (Aug 20, 2012)

Is it your C fuse that's blowing? If it is, and that's where your hot spot is, then your disconnect probably needs replacing (like others have said). It's old anyway.

Bussmann will tell you that your Fusetrons will tolerate hot connection points but to what degree I am not sure. It's possible you have hot spots with all your fuses but only one is hot enough to blow a fuse. That might explain why the disconnect is hot to the touch.


----------



## running dummy (Mar 19, 2009)

Is there a cooling unit on the compressor? I had a customer with an Ingersoll Rand rotary that would blow fuses. Their tech came out and said it was getting too hot. 

Funny thing is the cooling unit was part of the original package and it was never hooked up :huh: 

Sent from my SAMSUNG-SM-G900A using electriciantalk.com mobile app


----------



## MDShunk (Jan 7, 2007)

I'm betting on weak disco also, but in the mean time you might throw a set of clip clamps on everything to see if that helps them.


----------



## Bad Electrician (May 20, 2014)

when I ran service I use to keep a complete set of Fuse CLamps, have not seen them in some time.


----------



## Wirenuting (Sep 12, 2010)

I don't know if a screw compressor has an unloading valve, but if so, check it.


----------



## bobelectric (Feb 24, 2007)

Change the fusible disconnect in question,and if the compressor starts over 6 times an hour,I.R. recommends running it on unloaders.


----------



## GatewaySparky (Jul 23, 2010)

It is the C fuse that is blowing as far as I know. The screw compressor motor runs all the time and the compressor kicks in when air is needed to fill the reservoir tank. I'm pretty sure it has an unloader valve. If under pressure when you start it the unit will spray oil and water from a (unloader?) valve. 
The current is close on all phases line and load. Voltage drop from the disconnect to the mag starter is only about 4 volts.
The boss has gotten involved due to the frustration of the compressor owner and is calling the motor company who rebuilt the motor to come and check it. The boss mentioned something about "transformer action" at the utility line as a possible cause and that the amperages should be within 3-5% of each other. The last i checked TA is just how a transformer works. Is there more to this than the voltage drop / demand problem I have relayed to him?
The exhaust fan is used as the cooling unit and draws ambient air up through the casing. There is no refrigerant. An FOP test might be in my future....
Thank you for all your input on my problem. This is a great forum.


----------



## GatewaySparky (Jul 23, 2010)

Just to update. We lost the customer and he didn't think the disconnect was the problem. He's got a buddy in maintenance at Boeing who claims to know exactly what's the problem, and that we don't know what we are doing.


----------



## 99cents (Aug 20, 2012)

GatewaySparky said:


> Just to update. We lost the customer and he didn't think the disconnect was the problem. He's got a buddy in maintenance at Boeing who claims to know exactly what's the problem, and that we don't know what we are doing.


That sucks. I was kind of interested to see how this turned out. Betcha Mr. Boeing ends up replacing the disconnect.


----------



## GatewaySparky (Jul 23, 2010)

99cents said:


> That sucks. I was kind of interested to see how this turned out. Betcha Mr. Boeing ends up replacing the disconnect.


Me too.


----------

