Duct heater not working

[paul]

I'm supposed to wire up the controls for this duct heater. It doesn't say anything in my specs about t-shooting exisiting problems. :lol:

I'm thinking I'll see if there's anything in the coils to cause this fuse to blow out like it did before I re-apply power to it. I don't think I've seen a fuse blow this violently before.



Click picture to enlarge

 

[don_resqcapt19]

Paul,
That looks like a melt down from a poor connection at the upper fuse clip. There are a number of electrical parts connected together and a poor connection at any point will lead to excessive heat.
Don

 

[al hildenbrand]

Maybe it was a quality control "thing" and this one fuse slipped through without filler. . .

I look at that image and I see a plasma arc in the middle of the fuse that sustained for some time, enough time to allow a fairly columnated plume of heat and smoke to rise pretty straight up. And I'll bet this was at a running current level. And I'll bet that the arc moved around on the carbonized remains of the fuse.

 

[LawnGuyLandSparky]

Yes, that fuse didn't suddenly and violently blow. It was overheating for a long time.

Also check that there are 3 elements, and that one is connected to phase A-B, another to B-C, and the third to C-A. These duct heaters are coming from Mexico and some yet unnamed countries now, where quality control isn't exactly job #1.

 

[paul]

I haven't seen where it is from. It's been in the building since it was new in 1988. I was told by the mechanical contractor I'm working for to not touch it. Hook it up as is. They're afraid if they touch it, they're responsible for a warranty on this stuff. They tried to get the owner to upgrade the AHU's, but he decided that's where he wanted to cut the corners. I had to install the averaging sensor in one today and it was a fricking nightmare. Grease and dirt everywhere in the AHU, plus the cooling coils were full of mold and mildew. YUCK! I pointed it out to the GC on the job and continued on.

The duct heater was still functioning when they shut it down. That bank was one of three stages. So they still have two other stages plus the elements for BC on this stage. They even went so far as to tell me not to even pull the blown fuse out. I don't like it, but sometimes you just hafta do what you're told to do and move on. The electrical contractor on the job won't even mess with it, cus they don't want the liability either.