Sparkplug HV standards

If you enclose the plug too tightly, it will not work - think of a miner's Davey lamp.

On a cooker or similar it can be exposed to touch, so  long as the exposed shock energy is limited - off the top of my head I can't recall the energy and pulse rate allowed but it is more than enough to light a typical gas flame.

This is normally done by a capacitor of known charge, being dropped into coil of limited core cross section.. The other concerns are emc and if it the same electrode is dc biassed if it is also  used for flame detection.

Mike

Agree, any common type of spart plug will have very limited energy and despite the voltage is most unlikely to be dangerous. (avoid touching though as it will hurt, and might be dangerous under some unlikwly conditions)


I would treat an 11KV DNO overhead line with a great deal more respect than a spark plug operating at several times that voltage.


Remember that almost every motorcycle has one or two high voltage spark plugs withing easy reach, the high voltage connections are accessible without a key or tool. And how many motorcyclists are killed by shocks from the ignition system ?

I assume that the spark plug in question resembles an automotive one (or even lawnmower/chainsaw/etc). I have had a few belts off a spark plug lead and I would say that one off the 230 V mains is worse.


I wouldn't be worried about the exposed tip of a spark plug. Access is pretty limited when you bear in mind that the earth electrode(s) keep fingers away.


The socket on top of an old-fashioned coil in a motor car (or even more old-fashioned magneto) is only IP2X.


Depending upon how the voltage is produced, surely the biggest risk would come from a defective cable, but from the sound of it, the cable is enclosed.

Hi all thanks for your replies.


 I’d be interested to know what the shock energy limits actually are in terms of protecting people from harm - also thinking about people with pacemakers not that this project will ever be used by the general public!  If you know where I can find that info then let me know.


Cheers

In modern cars the spark plugs and leads (or coil packs) are now inaccessible to protect the owner doing any home maintenance easily. They are covered by a big unnecessary plastic cover that prevents easy entry to the H.V. cables and hot engine parts. This big plastic cover is designed to cause engine parts to overheat so adding to the local garage's profits.


Z.

depending on the application you may find things like the standards for electric fences in public places are helpful. (bounding voltages and energies of 10kV and 10 joules per pulse from memory.) No insulation there. Personally I consider the effects of the jump reflex from 10J to be also hazardous indoors, and we use a 1J action limit in the facility at my place of work, such that above that safety measures must be taken or their absence carefully justified.


Also in terms of not quite relevant standards, intended  for exposed voltages appearing on accessible surfaces like the connectors for domestic appliances like TVs and so on IEC 62368-1 defines permitted exposure limits ES1 that requires no safeguards for anyone, and ES2 that warrant at least  a single layer of protection for ordinary persons, and none for skilled or instructed. There is also a higher level ES3 that requires 2 levels of protection for ordinary persons or instructed persons, and 0 or 1 layer for a skilled person such as a repair technician.

The lmits roughly lines up with the double fault to danger in BS7671 above ELV, but not perfectly.

"ES1 and ES2, for any voltage up to the limit voltage, there is no

limit for the current. Likewise for any current up to the limit current, there is no limit for the

voltage. However, for ES1 and ES2, in no case can both the current limit and the voltage limit

be exceeded. ES2 is an energy source where both the voltage and current exceed the limits

for ES1, but do not exceed the limits for ES2. ES3 is any source where both the voltage limit

and current limit exceed ES2."


ES1 is current up to 2mA at any voltage or 60V at any current

ES2 is the same but 25mA or 120V

there are also pulse limits but they are complex.
"Single pulse limits - Where the electrical energy source is a single pulse, the energy source is classified from both

the voltage and the duration or from both the current and the duration. Values are given in

Table 8 and Table 9. If the voltage exceeds the limit, then the current shall not exceed the

limit. If the current exceeds the limit, the voltage shall not exceed the limit. Currents are

measured according to 5.7. For repetitive pulses, see 5.2.2.5."


More usefully for your ignition there are capacitor discharge limits as well
Table 7 – Electrical energy source limits for a charged capacitor

C(nF) ES1 Upeak(V)  ES2 Upeak(V)
300 or greater 60 120

170 75 150

91 100 200

61 125 250

41 150 300

28 200 400

18 250 500

12 350 700

8,0 500 1 000

4,0 1 000 2 000

1,6 2 500 5 000

0,8 5 000 10 000

0,4 10 000 20 000

0,2 20 000 40 000

0,133 or less 25 000 50 000

Linear interpolation may be used between the nearest two points.


These do seem a bit low if you actually want to light something,

Excellent reply thank you!