Why do lamps blowing trip RCDs?

[NickD]

...cos if the lamp is in effect Class II with connections only to L and N (Edison screw; standard bayonet cap in unearthed pendant or batten), you would naively think there is no way the L and N can be in imbalance. But still the RCD trips. Definitely talking RCD trips here not MCB. I've seen mention of surge current spikes but never got to the bottom of it. Googling just seems to bring back forum postings that don't really answer the question. Cheers.

 

[HappyHippyDad]

The rcd is a finely balanced unit relying on a very small imbalance between L and N ...when a filament lamp blows sometimes it leaves an ionised path through the gas atoms which act like a short circuit although it does collapse fast it can sometimes exceed the time/curve graph of the mcb.... as with any short circuit 1000's of amps may flow and the magnetic field associated with this is very large and can saturated the fine balancing fields of the rcd causing it to trip.

I wish there was something more than a 'like' I could give this!

 

[Badged01]

If you want to get technical about it and correct me if I'm wrong, current flows from positive / Line to negative / Neuteal and to complicate it the electrons flow from negative to positive, but you should know that.

I think you are confusing conventional flow ( + to - ) with actual electron (electric) flow (- to + )?

 

[spark 68]

I wish there was something more than a 'like' I could give this!

Oer missus! lol
Now, now, HHD we will have not of that kind of talk on here, this is a respectable forum I will have you know! lol

 

[telectrix]

If you want to get technical about it and correct me if I'm wrong, current flows from positive / Line to negative / Neuteal and to complicate it the electrons flow from negative to positive, but you should know that.

ah, but do the electrons know it? could be sometime they'll find out that for years they've been flowing the wrong way, then all become heterosexual.

 

[uksparks]

I think you are confusing conventional flow ( + to - ) with actual electron (electric) flow (- to + )?

I was just trying to be clever but it's not advisable when you have limited knowledge, it's a bit like telling a joke when you don't know who's knocking at the door yourself!

 

[Deleted member 72666]

Oer missus! lol
Now, now, HHD we will have not of that kind of talk on here, this is a respectable forum I will have you know! lol

It's okay as it's after the watershed!

 

[telectrix]

now why do you go mentioning plumbers?

 

[Deleted member 72666]

I was just trying to be clever but it's not advisable when you have limited knowledge, it's a bit like telling a joke when you don't know who's knocking at the door yourself!

Knock knock?...

 

[Deleted member 72666]

now why do you go mentioning plumbers?

...Soz!

 

[uksparks]

Oer missus! lol
Now, now, HHD we will have not of that kind of talk on here, this is a respectable forum I will have you know! lol

Now, you say that but others seem to suggest otherwise...

I didn't post it on here for people like you to have something to watch in your chair while jacking off to a forum

 

[spark 68]

It takes all sorts I suppose. lol

 

[Badged01]

Now, you say that but others seem to suggest otherwise...

If he wants to get into that 'jacking' stuff he must have been thinking of proton theory not electrons!

 

[Darkwood]

Oh right so not inductive effect so much as large fault current causing magnetic effects in/around the RCD coil and upscrewing it. Gotcha. Many thanks.

Well not exactly in your sense but the monitoring coil rely on induction to work so yes as well.