Why are switches being rated at different amps ?

I see lots of them on ebay rated for 10 maps at 240 volts and 20 amps at
120 volts.

Looks to me they should have the same amp rating at all voltages. The
do not specify any kind of load like something that would draw a larger
current at startup with a higher voltage.

On 2/16/19 5:29 PM, Ralph Mowery wrote:


Why are switches being rated at different amps ?

I see lots of them on ebay rated for 10 maps at 240 volts and 20 amps at
120 volts.

Looks to me they should have the same amp rating at all voltages. The
do not specify any kind of load like something that would draw a larger
current at startup with a higher voltage.


It's because of the arc ratings on switching to off.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

On 2/16/19 6:29 PM, Ralph Mowery wrote:


Why are switches being rated at different amps ?

I see lots of them on ebay rated for 10 maps at 240 volts and 20 amps at
120 volts.

Looks to me they should have the same amp rating at all voltages. The
do not specify any kind of load like something that would draw a larger
current at startup with a higher voltage.


'tain't the turn-on that's the issue, it's the turn-off. That's why
fuses rated at 250VAC are also rated at 32VDC.

A friend of a friend was severely injured a couple of weeks ago by an
arc flash at a 480V breaker panel. Turning off high-energy circuits is
no joke.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Ralph Mowery wrote:


Why are switches being rated at different amps ?

I see lots of them on ebay rated for 10 maps at 240 volts and 20 amps at
120 volts.


** The same switch is likely rated at 20 maps for DC switching up to 24V. Above that voltage, contact to contact arcing will become very severe or continuous.


Looks to me they should have the same amp rating at all voltages.


** You gotta be kidding.

Inrush surge capacity is another matter, requiring both heavier contacts plus a strong switch off force to pull contacts apart that have become slightly welded.



..... Phil


..... Phil

In article ,
says...

A friend of a friend was severely injured a couple of weeks ago by an
arc flash at a 480V breaker panel. Turning off high-energy circuits is
no joke.




I have seen the results of a 480 volt 3 phase 'blow up', Fellow at work
turned on a breaker that was only a 20 amp rating for a small motor.
Not sure what hapened, but it melted down a whole bank of about 30 or 40
cubicals in a load control center. That bank ws fed with around 400
amps from a larger breaker in what we called a substation room. It
meleted out the bus bars on that load control center.


When working I dealt with 480 V 3 phase equipment almost daily. Lots of
10 to 100 hp motors and some heaters that were fused at 250 amps.

On 2/16/19 7:53 PM, Ralph Mowery wrote:
In article ,
says...

A friend of a friend was severely injured a couple of weeks ago by an
arc flash at a 480V breaker panel. Turning off high-energy circuits is
no joke.




I have seen the results of a 480 volt 3 phase 'blow up', Fellow at work
turned on a breaker that was only a 20 amp rating for a small motor.
Not sure what hapened, but it melted down a whole bank of about 30 or 40
cubicals in a load control center. That bank ws fed with around 400
amps from a larger breaker in what we called a substation room. It
meleted out the bus bars on that load control center.


When working I dealt with 480 V 3 phase equipment almost daily. Lots of
10 to 100 hp motors and some heaters that were fused at 250 amps.





It's good to wear the Nomex suit and helmet when hacking with that
stuff. The FOAF was burned over more than 50% of his body.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On Saturday, 16 February 2019 23:29:11 UTC, Ralph Mowery wrote:
Why are switches being rated at different amps ?

I see lots of them on ebay rated for 10 maps at 240 volts and 20 amps at
120 volts.

Looks to me they should have the same amp rating at all voltages. The
do not specify any kind of load like something that would draw a larger
current at startup with a higher voltage.

higher voltage means more energy in the arc for a given current. It also means more ability to sustain the arc. DC is more able to sustain an arc than ac, for the same v,i.


NT

On Sat, 16 Feb 2019 19:57:46 -0500, Phil Hobbs
wrote:

On 2/16/19 7:53 PM, Ralph Mowery wrote:
In article ,
says...

A friend of a friend was severely injured a couple of weeks ago by an
arc flash at a 480V breaker panel. Turning off high-energy circuits is
no joke.




I have seen the results of a 480 volt 3 phase 'blow up', Fellow at work
turned on a breaker that was only a 20 amp rating for a small motor.
Not sure what hapened, but it melted down a whole bank of about 30 or 40
cubicals in a load control center. That bank ws fed with around 400
amps from a larger breaker in what we called a substation room. It
meleted out the bus bars on that load control center.


When working I dealt with 480 V 3 phase equipment almost daily. Lots of
10 to 100 hp motors and some heaters that were fused at 250 amps.





It's good to wear the Nomex suit and helmet when hacking with that
stuff. The FOAF was burned over more than 50% of his body.

Cheers

Phil Hobbs

They say that those make good body bags.
--
Boris

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