Coil fuse in elevator control blowing out too often

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PetrosA

Senior Member
I have a customer with a storage business. There is a relatively new (under 2 years old) hydraulic type elevator installed with a 5A slow-blow fuse protecting the coil of the contactor which controls the motor for the hydraulics. This fuse is blowing out a few times per month with no obvious cause. I've taken current readings multiple times and everything seems within spec. Any ideas as to why this might be happening? The installer is located in CA and getting one of their techs out to the East Coast evidently costs a lot more than me guessing at it repeatedly ;)
 

templdl

Senior Member
Location
Wisconsin
Confirm that it is the correct fuse for the application first. If so I would check he amperes to see if them correspond to the coil's rated current. If they do my next target would be the control circuit to assure that what ever is controlling the closing of the contactor is not chattering that when the contactor closes it closes.
Thus you would be eliminating the obvious.
 

Open Neutral

Senior Member
Location
Inside the Beltway
Occupation
Engineer
This fuse is blowing out a few times per month with no obvious cause. I've taken current readings multiple times and everything seems within spec. Any ideas as to why this might be happening?


AC contactors draw lots more current when closing than once closed. Are you sure it is fully closing every time?
 

PetrosA

Senior Member
@templdl - I have not noticed chattering during any of my visits, but that was one thing I suspected, although I was thinking in terms of voltage issues. I think your advice is good and when I get called back I'll look into it.

@Open Neutral - The contactor seemed to be engaging fully and staying engaged. If it's disengaging, it must be a random thing.

@ptonsparky - The stock market would have to do some serious magic for me to retire any time soon ;) At 42, I'm trying to learn enough to keep me going for the second half of my life. I'll check the clips too the next time I go back.

I've recommended that they get a service guy from the elevator company out, but I won't be surprised to get a call back anyway, so I'm trying to get a better understanding of the system. Thank you all for your help!
 
T

T.M.Haja Sahib

Guest
@Open Neutral - The contactor seemed to be engaging fully and staying engaged. If it's disengaging, it must be a random thing.

Open Neutral gave a valid suggestion.You gave a dumb reply.If the contactor is not fully engaged,the running coil current may exceed the fuse rating and hence this may cause the fuse blowing after some time.Check the running coil current.:dunce:
 

iwire

Moderator
Staff member
Location
Massachusetts
I have a customer with a storage business. There is a relatively new (under 2 years old) hydraulic type elevator installed with a 5A slow-blow fuse protecting the coil of the contactor which controls the motor for the hydraulics. This fuse is blowing out a few times per month with no obvious cause. I've taken current readings multiple times and everything seems within spec. Any ideas as to why this might be happening? The installer is located in CA and getting one of their techs out to the East Coast evidently costs a lot more than me guessing at it repeatedly ;)

Just a out of left field thought, has anyone confirmed the voltage being supplied to the coil is the voltage the coil requires?

What I mean is, maybe it was the wrong coil from the start.


BTW, here I would have my ass handed to me for touching anything beyond the disconnecting means for an elevator. Can you legally work on this and if so do you want that liability?

Just saying .....

(I also second open neutrals suggestion.)
 

topgone

Senior Member
Just a out of left field thought, has anyone confirmed the voltage being supplied to the coil is the voltage the coil requires?

What I mean is, maybe it was the wrong coil from the start.


BTW, here I would have my ass handed to me for touching anything beyond the disconnecting means for an elevator. Can you legally work on this and if so do you want that liability?

Just saying .....

(I also second open neutrals suggestion.)

Yep, fuse holders used to get me waking up at night in my other life before. Easy to see the clips discolored or smoking hot if loose.

To be sure we get all bases covered, how about replacing the fuse and the contactor coil at the same time. I am guessing the coil could have some coil-to-coil shorts causing the fuse to blow. If the contactor is noisy, replace that also.
OTOH, we might end up replacing the whole starter!:lol:
 

PetrosA

Senior Member
Thanks for the ideas. This is a freight only elevator so I think it's ok for me to change the fuses :) I didn't see any signs of the fuseholder heating up and IIRC it was only drawing about 1.4-1.6A max, depending on which clamp I used. I'll print this thread out and keep it in my truck for when I get called back.
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
What supplies this control circuit? A control transformer? Is there anything else on the secondary of the control transformer?
 

PetrosA

Senior Member
What supplies this control circuit? A control transformer? Is there anything else on the secondary of the control transformer?

Honestly I didn't dig that deeply but I believe the coil is 120V coming off of a relay. It's a tight control box with all the wiring in small cable ducts from both up/down stations, hinged door sensors, roller door sensors, pressure sensors (from the hydraulic lines) and e-stops plus pilot lights at the two up/down stations and all the line voltage wiring. If I have to, I'll start opening stuff up next time.

I'm not real well versed in this kind of control stuff but I think if I take the time to trace it and draw it all out next time I should get a better understanding of it. I'll probably have to eat some billable time on it though ;)
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
In a number of elevator controls I have seen, the coil is rated for the line voltage, or if the line is 208V 3Ph 4W they use Line and Neutral on a 120V coil. If it's a weak system and because the elevator is often the largest motor in the building, sometimes the act of closing the contactor and engaging the motor is the exact thing that causes the voltage drop, that then causes the coil to chatter and that can indeed blow the fuses. The thing is, if this only happens when the line voltage is already low for some other reason, it's pretty difficult to find the problem unless you just happen to be there when it happens.

Start by checking that the coil voltage does indeed match the control circuit voltage as the others mentioned. Then learn everything you can about the control circuit design, i.e. what I said above. If it is a line voltage coil, and maybe even if not, see if anyone can give you a history of when the fuses blow and look for a pattern. For example on one that I worked on, the VD only happened when the maintenance shop was running their air compressor AND someone used the elevator. Thing was, they only used the air compressor a couple times per week and only after hours, so the combination of events was pretty rare. I just happened to be there when they ran the compressor and I saw the lights flicker. When I went over and hit the elevator button, the contactor chattered.
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
The couple of times I got suckered into working on elevators it was a nightmare. No schematics, everything jammed in there tight, and a boss calling every 1/2 hour wanting to know "IS IT RUNNING YET, WHAT'S TAKING SO LONG?"

The worst I ever saw was Philadelphia City Hall. We had the emergency generator contract. The generators were on the roof and the transfer switches were in the elevator machinery rooms. All old DC machines from like 1920 or something. My boss at the time wanted me to bid on the elevators, I was like no way, never never never. Everything in the control panel was a big hacked up mess, covers missing, wire so old I was afraid to breathe on it hard let alone touch it.

Whoever was fixing them probably knew the system really well and could get in and out without touching too much. If I had gone in there and tried to trace stuff all the insulation would have been laying in the bottom of the cabinet and there would have been nothing but a big mass of shorts
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
In a number of elevator controls I have seen, the coil is rated for the line voltage, or if the line is 208V 3Ph 4W they use Line and Neutral on a 120V coil. If it's a weak system and because the elevator is often the largest motor in the building, sometimes the act of closing the contactor and engaging the motor is the exact thing that causes the voltage drop, that then causes the coil to chatter and that can indeed blow the fuses. The thing is, if this only happens when the line voltage is already low for some other reason, it's pretty difficult to find the problem unless you just happen to be there when it happens.

Start by checking that the coil voltage does indeed match the control circuit voltage as the others mentioned. Then learn everything you can about the control circuit design, i.e. what I said above. If it is a line voltage coil, and maybe even if not, see if anyone can give you a history of when the fuses blow and look for a pattern. For example on one that I worked on, the VD only happened when the maintenance shop was running their air compressor AND someone used the elevator. Thing was, they only used the air compressor a couple times per week and only after hours, so the combination of events was pretty rare. I just happened to be there when they ran the compressor and I saw the lights flicker. When I went over and hit the elevator button, the contactor chattered.


That is what I was thinking, But I was thinking maybe a control trans too small to handle the contactor inrush when there is a low normal voltage condition in the building
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
That is what I was thinking, But I was thinking maybe a control trans too small to handle the contactor inrush when there is a low normal voltage condition in the building
It's possible, but generally storage building hydraulic elevator motors are under 20HP, even the smallest good quality CPT can handle a Size 2 contactor coil. Plus if it was working, why would it have changed?

But still, if it is too small AND/OR the supply is too weak, that might do it. Sometimes in old or poorly designed office buildings, tennant improvements and more office machines than anticipated will build up over time and put you in that situation. In a storage facility, it might be that renters are putting in heaters or doing work in their units and over taxing the system.
 

PetrosA

Senior Member
Problem found

Problem found

Here's an update to the thread. The owner got an elevator company in to check it and it turns out the control cable in the shaft was shorting intermittently. I wouldn't have found this in a million hours, so I guess it's a good idea to bow out when you feel over your head sometimes :)
 
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