what are "Snap Switches" as mentioned in 408.36(A)

[mshields]

Silly question. Is a regular old MCCB a snap switch.

and if it is, what is 408.36(A) telling us. If you have a 30A-3P breaker in a DP, you may not have a 225A-3P breaker in that same DP.

 

[kwired]

Silly question. Is a regular old MCCB a snap switch.

and if it is, what is 408.36(A) telling us. If you have a 30A-3P breaker in a DP, you may not have a 225A-3P breaker in that same DP.

My guess is they are talking mostly about the old panelboards with fuses - and a corresponding switch for disconnecting each fuse holder.

 

[Smart $]

I thought a snap switch was the old type of wall switch and it's close cousins. The used to be spring loaded... and they went "snap" when flipped 'em (not as in broken; just an audible indicator of the switch's change in state). Then came the silent switch, which they basically just removed the spring, called it the new and improved version... and charged you more for it. :slaphead:

 

[kwired]

I thought a snap switch was the old type of wall switch and it's close cousins. The used to be spring loaded... and they went "snap" when flipped 'em (not as in broken; just an audible indicator of the switch's change in state). Then came the silent switch, which they basically just removed the spring, called it the new and improved version... and charged you more for it. :slaphead:

Most molded case circuit breakers have springs as part of the operating mechanism and do snap when you manually operate them - but are not a snap switch to the NEC.

Getting back to what I mentioned before - I recall a few places in the past that had old Frank Adams fuse centers - they had pullout fuse blocks for cartridge fuses, but the plug fuses all had a switch for each fuseholder that removed power to the fuseholder.

 

[infinity]

Very popular 50-75 years ago. Removed quite a few of these recently at the United Nations building.

 

[ptonsparky]

I thought a snap switch was the old type of wall switch and it's close cousins. The used to be spring loaded... and they went "snap" when flipped 'em (not as in broken; just an audible indicator of the switch's change in state). Then came the silent switch, which they basically just removed the spring, called it the new and improved version... and charged you more for it. :slaphead:

They had an AC and DC rating. Higher HP as well, IIRC.
Tungsten comes into mind as well.

 

[steve66]

Silly question. Is a regular old MCCB a snap switch.

and if it is, what is 408.36(A) telling us. If you have a 30A-3P breaker in a DP, you may not have a 225A-3P breaker in that same DP.

The handbook explains that it does not apply to circuit breakers.

A snap switch is basically a light switch. They also mention them in 430 where snap switches can be used as disconnects for low HP motors.

 

[charlie b]

The article 100 definitions that include the word "switch" are not helpful. My understanding is that if a device has its own mechanism for overcurrent protection, then it is not a switch. I believe that the term "snap switch" covers the majority of all switches that we encounter. The terms "knife switch" (the most common construction for disconnect switches), "rotary switch," and "dip switch" cover most of the others.

 

[Jraef]

Look at post #5 in this thread.
http://forums.mikeholt.com/showthread.php?t=99204

Same thing infinity posted. This is what they are referring to.

As opposed to this, which is NOT a "snap" switch:


It's a reference to a relic in what used to be used before CBs became the norm. But for all intents, the purpose of this code section is, as I was told many moons ago, to force people to no longer use those old snap switch fused panels on larger services, so they added the rule maxing it out at 200A. It basically removed them from being usable on commercial and industrial applications where there was more fault current available. Those snap switches were not automatic, so they had no coordinated interrupt capacity, they relied on the fuses. It was therefore theoretically possible to open them under fault conditions (while waiting for the fuse to clear for instance) that could cause the switch to explode on you in the process.

I was involved in a project at a US Steel plant in the late 70s where we had to go through and rip out all of these we could find, working or not. When they were installed around WWII, the service transformers for the offices where they were used were separate from the service drops for the mill itself, but had been combined to save money in the 60s. So the fault current available on them was >30kA, as opposed to being under 10kA originally.

 

[mshields]

interesting

interesting

thanks

 

[dkidd]

There is an article discussing them at http://www.ecmag.com/section/codes-standards/understanding-snap-switch-installation-requirements