Re: Arcing

[Dambo]

Hi there. Quick question - With regards light switches, what is arcing? and how does it occur?

 

[Apache]

The 'arc' is is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air.

It's the flash you see jumping from the contacts usually when a light is switched off.

see here for more

And hence why we leave the switch as it is when we smell gas!

 

[Dambo]

Does that basically mean that current could then still flow even in the off position?

 

[Apache]

Does that basically mean that current could then still flow even in the off position?

No. It just happens when the conductors are very close, ie the moment the switch is opened (or closed).

When an inductive circuit is switched off the current cannot instantaneously jump to zero; a transient arc will be formed across the separating contacts

 

[Dambo]

Ah, I see. Is this then caused by a deterioration of the switch mechanism i.e. contacts?

 

[Apache]

Ah, I see. Is this then caused by a deterioration of the switch mechanism i.e. contacts?

No it's a normal occurrence.

See my last post "When an inductive circuit is switched off the current cannot instantaneously jump to zero; a transient arc will be formed across the separating contacts"

 

[Dambo]

Am I right in saying that the quicker / more efficient the switch mechanism the less likely it is that dangerous arcing will occur?

 

[Andy™]

Does that basically mean that current could then still flow even in the off position?

yes, but only for a split second until the gap is too far for the electric to arc over.

 

[spinlondon]

Arcing causes deteriation of the switch contacts.

 

[sellers]

also, light switches and other switches are rated to deal with arcing and operating. They are rated to switch a maximum amount of current before the switch will deteriate or operate dangerously.

For example a light switch may be rated at 10amps, and a double pole isolator at 100amps.

 

[Dambo]

also, light switches and other switches are rated to deal with arcing and operating. They are rated to switch a maximum amount of current before the switch will deteriate or operate dangerously. For example a light switch may be rated at 10amps, and a double pole isolator at 100amps.

Can you just explain the bit about the 10amps light switch and 100amps double pole isolator Sellers, I'm a wee bit confused by that

 

[Apache]

Can you just explain the bit about the 10amps light switch and 100amps double pole isolator Sellers, I'm a wee bit confused by that

It's the rating of the particular switch, ie the load it can handle safely for prolonged periods.

 

[Dambo]

Thanks Apache!

 

[kme]

FYI

On DC circuits, it isn`t unusual to find small permanent magnets located to either side of the contact gap. The field created by the magnets "throws" the spark away from the contacts, thereby extending their usable lifespan.

(I first saw these on 400A open contactors, used for fork-lift trucks.)

 

[nic00b]

FYI

DC = Nice Flash / Loud Bang .... As an apprentice it scared the hell outta me going into some of the subs with large DC panels

 

[Pyro]

This link will (should) take you to some fine examples of some heavy-duty arcs and sparks, as well as some nice background reading on the subject!

http://205.243.100.155/frames/longarc.htm

The 500kV disconnect switch and the exploding transformer are my favourites]

 

[Megaohm7]

Arcing causes deteriation of the switch contacts.

Is silver used on the contact points ?