Kettle Elements And Safety

[Online Brewing Supplies]

I am interested on the opinion from some electrically qualified person to explain how a electrical heating element that is fitted to a metal kettle is earthed if it only has two wires fitted like many on Ebay?
I ask this because I have a similar set up with a three wire element system (Earth included) fitted and last brew it tripped my safety switch twice and shut down the system. This happened with a qualified electrician present yet we could not find a fault.
How would I be if I did not have a safety switch and an earth ?
Thanks
GB
Edit for clarity.

 

[matho]

hey gryphon,
from what i understand most heating elements are a nichrome wire inside a tube with magnesium oxide between the two just like 'pyro' cable.
when dry magnesium oxide has a very high resistance so it insulates the outside tube from the nichrome element, unfortunately magnesium oxide is hyrdoscopic and once it is wet it goes low resistance allowing current to go to earth tripping off the rcd. It only takes 30mA to trip off the rcd which is about 10,000 ohms of resistance.

now how can water get to the magnesium oxide is the question, it is sealed up with gaskets at the end where the wires enter the element and is inside a water tight tube, so either it is coming thru the gaskets or the tube.

i know from my days of check electrical circuits that if you were meggering the circuits the insulation resistance had to be above 1 Mohm or it was a defect the only exception was the hot water heater circuit which was allowed to go as low as 100 Kohm, so they obviously become leaky over time.

the question is did your sparky mate megger the element between the active and the metal tube of the element?

CHEERS MATHO

 

[Online Brewing Supplies]

hey gryphon,
from what i understand most heating elements are a nichrome wire inside a tube with magnesium oxide between the two just like 'pyro' cable.
when dry magnesium oxide has a very high resistance so it insulates the outside tube from the nichrome element, unfortunately magnesium oxide is hyrdoscopic and once it is wet it goes low resistance allowing current to go to earth tripping off the rcd. It only takes 30mA to trip off the rcd which is about 10,000 ohms of resistance.

now how can water get to the magnesium oxide is the question, it is sealed up with gaskets at the end where the wires enter the element and is inside a water tight tube, so either it is coming thru the gaskets or the tube.

i know from my days of check electrical circuits that if you were meggering the circuits the insulation resistance had to be above 1 Mohm or it was a defect the only exception was the hot water heater circuit which was allowed to go as low as 100 Kohm, so they obviously become leaky over time.

the question is did your sparky mate megger the element between the active and the metal tube of the element?

CHEERS MATHO

We used a very expensive Fluke (2k +) and did a few test's but to be sure if we did that test you mentioned I will have to ask. I will let you know.
GB

 

[Jono_w]

We used a very expensive Fluke (2k +) and did a few test's but to be sure if we did that test you mentioned I will have to ask. I will let you know.
GB

Matho is spot on,
This happens a fair bit if the element has not been used in a little while and absorbed some moisture, if it continues I would be getting it's insulation resistance tested again.
I have seen elements that have exploded due to the build up of pressure inside them because of excess moisture.

 

[dent]

We didn't megger the heating element - the reason the RCD tripped was that the active conductor on the bottom of the HLT was exposed and touched the metal of the brewing frame - which was luckily earthed. The wiring underneath the HLT has since been insulated more effectively.

The fluke installation tester was used to check the earthing of the HLT and brew frame - the HLT was earthed with a lug attached to the earth conductor.

Appliances with only two pins on the plug are generally double insulated (Class II Equipment). I'm not convinced the cheap elements have been built to this standard though, I'm not sure. I would, in any case if possible, earth the metal of the container the element is mounted in. This would insure that the kettle cannot become live even if a hole was made in the element sheath.

 

[Zizzle]

There is no doubt you should earth your brewing vessels, even if the element is a 2-wire job.

It's also worth mentioning that modern that you shouldn't confuse RCDs with ELCBs. RCDs measure the difference in current between the active and neutral lines not the current flowing through the earth wire. Which means even with no earth on your pot, it should still save you.

 

[Online Brewing Supplies]

There is no doubt you should earth your brewing vessels, even if the element is a 2-wire job.

It's also worth mentioning that modern that you shouldn't confuse RCDs with ELCBs. RCDs measure the difference in current between the active and neutral lines not the current flowing through the earth wire. Which means even with no earth on your pot, it should still save you.

Are RCD's fitted in every house ? If not what are your chances of getting electrocuted if some thing goes wrong and your systems not earthed ?
I have one (RCD) for my house another for my brew shed, very glad I have now.
GB

 

[Online Brewing Supplies]

Just checked the RCD law in WA and it looks like there would be a lot of older houses that dont have RCD protection.
Two RCDs protecting all power and lighting circuits must be fitted to a residential property before it can be sold and the transfer of title takes place. Penalties apply if RCDs are not fitted and the land title is transferred to another person.
GB

 

[matho]

not every house gryphon
the australian wiring rules were changed in the early 90's to say that every power circuit must have RCD protection and then a little bit later to every circuit must have RCD protection. So if you have a relatively new house you show have RCD protection. If your unsure go out to the meter board or your main switch board and have a look you should see something like this



if you dont the get a rcd protected power board like this



it is also an australian wiring rule that all metal enclosures that have electrical circuits in them must be earthed, so all electric metal kettles must be earthed and dont just think that because your element has an earth pin, that means your kettel is earthed. make sure it is earthed by running a wire from the earth pin to the kettle.

cheers matho

 

[newguy]

Are RCD's fitted in every house ? If not what are your chances of getting electrocuted if some thing goes wrong and your systems not earthed ?
I have one (RCD) for my house another for my brew shed, very glad I have now.

Around here, their presence depends on the age of the house. Anything built prior to roughly the early '70s doesn't have them. For a time 'the code' only required them in wet locations (bathrooms and to a lesser extent garages), and now kitchens also require them. I think that 'whole home' RCDs exist but I have a feeling that their cost is prohibitive.

The chance of being electrocuted is not zero but it's not exactly high either. I'm an electrical engineer and electricity just doesn't scare me but then again I (usually) know what to steer clear of. I have been shocked, many times, but only once that scared the hell out of me. With or without an RCD (never put blind faith in anything, particularly a life saving device like an RCD), it's best to just exercise caution. One of the first rules I was taught in the labs at university was the one hand rule. If dealing with energised circuits, always leave one hand at your side or behind your back. The point is that this makes an electrical path directly through your heart impossible, and that's what kills. Another rule is that if in doubt, use the back of your hand to touch the object in question. If it is live, the muscles in your hand can't involuntarily grasp onto it, effectively locking you in place. In fact, the muscles in your arm will often jerk your hand away from danger.

When this part of the world was first electrified, 3600V distribution networks were common (the high voltage lines feeding a neighbourhood). At that time, electrocution deaths were common if someone touched a line. After a time, 14,400V distribution networks started to replace the 3600V lines and the power companies noticed that deaths due to electrocution fell. The number of encounters/injuries remained the same but the deaths fell. However, the injuries were now almost all amputations. In hindsight, this makes sense. At 3600V, you grab on and can't let go - you just sit there and cook. At 14,400V, there's enough "oomph" to flash boil the moisture in your body, which tends to have the most prominent effect at the joints - which tends to blow them apart. This severs the circuit, which also tends to help save your life. Albeit missing a hand, or an arm or a leg (below the knee), or a foot, but you're alive.

 

[Online Brewing Supplies]

Thanks guys this advise could save lifes. I for one have learned a lot and I will also get one of those portable RCD power box's.
GB

 

[Zizzle]

I have been bitten a couple of times. Not by the mains directly, but by power supply capacitors holding charge.

Like newguy says, the real risk is that your muscles hold you onto the source of electrocution.

I remember being told an urban legend scare story when I was kid learning to weld: something about a guy welding on his own, managed to put his body in the circuit (probably not that hard with a red hot welding rod able to burn through the high-resistance dead skin layer) and was found days later as a pile of dry charcoal since the current had driven off all the water from his body.

Luckily most caps will discharge quickly enough to not defibrillate your heart, and obviously not be able to constantly provide power to keep your muscles involuntarily holding on to them. But they can still give you an almighty wallop.

Interestingly most RCDs work on the principle not so much of limiting the current that you take (30mA can cause defibrillation) but to limit the time of the current (you need 30mA+ for a quite a few milliseconds to cause defibrillation).

And remember that the dead/dry skin layer on you body won't always conduct and give you a big hit -- if you feel a tingle from anything, don't mess around, turn it off -- it could still be live with dangerous voltage -- luckily you just haven't conducted any of it through your heart and muscles yet.

 

[Greg.L]

If dealing with energised circuits, always leave one hand at your side or behind your back. The point is that this makes an electrical path directly through your heart impossible, and that's what kills. Another rule is that if in doubt, use the back of your hand to touch the object in question. If it is live, the muscles in your hand can't involuntarily grasp onto it, effectively locking you in place. In fact, the muscles in your arm will often jerk your hand away from danger.

I've had a few shocks from electric fences, these are much worse when the ground is wet. The worst thing is if you are grounded to a metal post, I have had a shock go in one arm and out the other, a real heart starter. Electric fences are pulsed so you can get away, your hand jolts back very quickly. They do run 6000v so can give you a pretty good shock. I always test them with a blade of grass.

Greg

 

[Online Brewing Supplies]

I've had a few shocks from electric fences, these are much worse when the ground is wet. The worst thing is if you are grounded to a metal post, I have had a shock go in one arm and out the other, a real heart starter. Electric fences are pulsed so you can get away, your hand jolts back very quickly. They do run 6000v so can give you a pretty good shock. I always test them with a blade of grass.

Greg

What was that thing on Myth Busters about some one pissing on an electric fence ? cant remember if he got a wollop or not ? Still I am not about to find out either.
What does the grass test do ?
GB

 

[Greg.L]

If you hold a green blade of grass with the other end flat on the wire, you will feel a tingle if the wire is live.

Greg

 

[Harry Volting]

I seem to recall Mythbuster Adam getting a zorch up the snake eye as he was muttering something. Serves him right. Fancy using yer knob as a test instrument.
I remember getting caught at a bucks night when I was a young bloke after asking where the best spot to have a piss was.
'Just over that fence, young fella'. Ha . Didn't drop my beer though.

 

[Online Brewing Supplies]

If you hold a green blade of grass with the other end flat on the wire, you will feel a tingle if the wire is live.

Greg

Pitty , no green grass over here for a few months yet, had our first rain this week in about 2 months.
GB

 

[Greg.L]

Pitty , no green grass over here for a few months yet, had our first rain this week in about 2 months.
GB

When the ground is that dry, electric fences don't work very well.

Greg