Why are the RCD trip times for I and 5I 300ms and 40ms

[Dave Jenkins]

Is there any particular reason why the trip times for RCDs at I and 5I are the values they are (300ms and 40ms).
Is there some particular medical reason why??
I'm just curious, no particular reason but may weave that into the conversation next time I'm in the pub!!

 

[Pete999]

Is there any particular reason why the trip times for RCDs at I and 5I are the values they are (300ms and 40ms).
Is there some particular medical reason why??
I'm just curious, no particular reason but may weave that into the conversation next time I'm in the pub!!

1 and51???

 

[static zap]

I think of it as energy managment to restrict damage to what ever is not being a good enough insultor .
( No designing them - so no hard facts !)

 

[Gakure]

For the safety purpose, the fatal current to human body is about 50mA although any current above 10mA can still cause some harmful effects. At 5 times rated current of 30mA (150mA) if human or livestock are exposed beyond 40ms is fatal.
At times of 30mA the body can withstand for upto 300ms but not more than that.
I believe there are better explanation out there but the main point is for safety purpose.

 

[westward10]

30ma for 40ms is the decided current/time that the average human body can withstand before damage or death will occur.
So the x1 test is for fault protection of a circuit and x5 is for additional protection to us humans.

 

[Rpa07]

I think it has been covered on previous posts but the 40ms is less than the frequency of a heartbeat so the rhythm cannot or may not be interrupted into arrhythmia (not good heart beat!) That may be dis rhythmia
Impresses the heck out of customers when you come out with that safety gem and the reason that they are putting their 'hard earned' into your mitt for a CU change!

 

[telectrix]

 

[Dave Jenkins]

Thanks guys...
I think the values are selected to reduce the current flow (as westward10 and others have suggested) rather than having anything to do with the actually heart beat/frequency.
I'd be interested to hear a medical explanation though....

 

[telectrix]

but who cares. we are just like specks of dust in the bigger picture of the universe.

 

[static zap]

In terms of thermal damage
(assuming we are mostly resistive and not capacitive- Microwaves love warming water)
30mA ..at 240V for 300ms aprox 2.1W
150mA ......................40ms aprox 1.44W ... so unlikely to give bad/deep burns
..on even small contact area.

Had pondered 30mA at 1/3 sec .. do some let go before RCD trips ?

 

[westward10]

Never assume an rcd will trip and save your life.

 

[static zap]

Never assume an rcd will trip and save your life.

Sods laws got that one covered ... it will be the cheap faulty one

 

[Richard Burns]

I think that Gakure is pretty close to the mark, (on average!!) a human can take 30mA for ~500ms or 150mA for 40ms through the body without muscle contraction so the disconnection times are probably set to those levels in the product standard. Obviously some livestock can take less than this and 30mA protection should cover them as well.
Generally on a direct line earth fault the current will be rising very fast up to the PEFC and so disconnection should be fast enough that the higher current will have less chance of causing irreversible effects. I am not sure of the rate of rise but as current on an ac circuit will peak every 10ms it must be in a similar timescale so 40ms sounds quite slow really.
You must have seen this graph of the effects of current in the human body:

 

[Dave Jenkins]

My gob is well and truly smacked!
Question answered - thank you...
..now if I can commit all that to memory...