OL relay necessary??

If i don't miss my guess, it would fit in the MPCB category, but I am wondering if there is some UL# that would tell us.
 
There is a difference between MPCB's & MCP MPCB's are fine on their own but MCP's must use an O/L as well I believe.
Yes, but if you enlarge that photo, you can see the thermal adjustment dial on the lower left side of each of them, making them MPCBs. The MCPs don't have that.
 
Actually NEC Article 430 states that you need both a branch circuit protector and a motor overload
And I could not find anything otherwise.
Branch circuit protection and motor overload are 2 completely different thing each is designed to do different things
Lets look at the overload
What is it for, to prevent the motor from drawing to much current ( Overloading) if the motor overloads the OL trips and if it’s wired correctly shuts off the motor. The overload can b in many forms the OL relay that is common, Manual starter overload combination that acts as both a starter and overload like the ones pictured here, they have morphed and changed over the years but basic concept is still the same. I have worked with most types including the old oil filled dashpots ( I dout anybody on this board have ever seen a dashpot OL)
NEC require some type of overload on all motor circuits except the small motors usually used in residential uses
In summary the overload is to disconnect the motor before it draws too much power and destroyers itself.
VFD’s have an electronic OL built in so and external one is not needed unless you are using the VFD to feed multiple motors then an OL is required for each motor.

Now lets look at the Branch Circuit Protectors
I have had the discussion may times before
I really think they should be called Branch Circuit Isolators because that what the do.
When they open they isolate the faulted branch from the main power source.

You must first understand there is no device available to disconnect any circuit before it faults ( Short circuit, ground fault whatever )
So the best you can do is to disconnect (Isolate) the branch as quickly as possible to protect the power source in a fault detection
With branch circuit protection you have 2 basic types the oldest and still the most reliable is the fuse then you have the modern CB circuit breaker I am not going to get into the different types they all work about the same different speeds , different current curves ect.
I have had panel shops tell me they don’t need a Branch Circuit Protector, their panels are to small to require one. What they forget is that when the panel is installed and powered from a plant main panel that main panel has a Branch Circuit Protector in it, the main panel breaker isolates the sub panel on a fault. So you actually have it anyway.
All circuits require a circuit protector from 5 V to 100KV transmission lines there is no exception to that.
A So if I have a client that insists that I don’t need either of them I walk away I don’t need that liability if something goes bad.
It always falls back to last person working on it.

To repeat both are required on all motor circuits.
 
Actually NEC Article 430 states that you need both a branch circuit protector and a motor overload
And I could not find anything otherwise.
Branch circuit protection and motor overload are 2 completely different thing each is designed to do different things
Lets look at the overload
What is it for, to prevent the motor from drawing to much current ( Overloading) if the motor overloads the OL trips and if it’s wired correctly shuts off the motor. The overload can b in many forms the OL relay that is common, Manual starter overload combination that acts as both a starter and overload like the ones pictured here, they have morphed and changed over the years but basic concept is still the same. I have worked with most types including the old oil filled dashpots ( I dout anybody on this board have ever seen a dashpot OL)
NEC require some type of overload on all motor circuits except the small motors usually used in residential uses
In summary the overload is to disconnect the motor before it draws too much power and destroyers itself.
VFD’s have an electronic OL built in so and external one is not needed unless you are using the VFD to feed multiple motors then an OL is required for each motor.

Now lets look at the Branch Circuit Protectors
I have had the discussion may times before
I really think they should be called Branch Circuit Isolators because that what the do.
When they open they isolate the faulted branch from the main power source.

You must first understand there is no device available to disconnect any circuit before it faults ( Short circuit, ground fault whatever )
So the best you can do is to disconnect (Isolate) the branch as quickly as possible to protect the power source in a fault detection
With branch circuit protection you have 2 basic types the oldest and still the most reliable is the fuse then you have the modern CB circuit breaker I am not going to get into the different types they all work about the same different speeds , different current curves ect.
I have had panel shops tell me they don’t need a Branch Circuit Protector, their panels are to small to require one. What they forget is that when the panel is installed and powered from a plant main panel that main panel has a Branch Circuit Protector in it, the main panel breaker isolates the sub panel on a fault. So you actually have it anyway.
All circuits require a circuit protector from 5 V to 100KV transmission lines there is no exception to that.
A So if I have a client that insists that I don’t need either of them I walk away I don’t need that liability if something goes bad.
It always falls back to last person working on it.

To repeat both are required on all motor circuits.


Both are provided by an MPCB.
 
Hi Gary, I came across them in the early 80's those were the days when you needed to carry an oil can lol. I remember some guys that worked on a gas compression site, the procedure for working on there was you could only take your vehicle in if it had suppressors fitted, no aluminium boxes to be bolted to steel frames, a pile of specs 5ft high if you were doing a project. kicked off site if you used the wrong screwdriver (each terminal had to be tightened with the correct size supplied or recommended by the terminal Mfr.). When I visited site the electricians carried oil cans, a box of matches (yes Matches but the heads cut off), I wondered what they were for, I found loads of them in the panels. Apparently they used them to force or help relays. so much for safety.
 
parky
I had a good chuckle on that match to help relays
I have actually see broom handles to force in a motor contactor
I remember a supervisor shoving a screwdriver into a lockout contactor for a conveyor while the guy was working on it he got clear I time and action taken for the supervisor if you complained you lost your job
 
parky
I had a good chuckle on that match to help relays
I have actually see broom handles to force in a motor contactor
I remember a supervisor shoving a screwdriver into a lockout contactor for a conveyor while the guy was working on it he got clear I time and action taken for the supervisor if you complained you lost your job

My favorite story on that front was when I was called out to spec a Soft Starter to replace an old failed Westinghouse Wye-Delta starter. The control circuit for the Y-D was screwed up somehow so it didn’t work, but the seal-in contacts still did. So they had two sticks, one painted blue, one brown, with corresponding colors on the contactors and a sign in the inside of the MCC door telling the operator to use the blue stick to push the blue one in first, count to three then push in the brown one. They had been using it that way, 3 times per day, for at least 5 years...

That was about 15 years ago and I recently visited that user site where I related that story to their crew. They said they had heard about it but everyone involved had retired long ago, so they were not sure if it was real. I have pictures on a hard drive somewhere that I’m going to send them.
 
Originally posted by GaryS:

To repeat both are required on all motor circuits.

I don't think anyone is saying that both of these functions are not required. They most certainly are. However, what some of us ARE saying is that if the devices truly are motor protection circuit breakers (jraef's eyes are much better than mine) that the device encapsulates both functions in one device.

Keith
 

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