Electrical hazards and safety precautions for enclosures.

Postby froot » Thu Jul 19, 2007 5:57 pm

You get 2 different breakers, an earth leakage and a simple circuit breaker. An earth leakage breaker trips when there is more than 20mA current flowing through the earth which is very low, but it doesn't monitur the current on the live and neutral. That's the job for the circuit breakers. Those you can get with either of 2 different 'curves'. This means that it is designed to trip after preset amounts of time at full rated load. The one tolerates full load current for longer than the other.
Pythonodipsas, depending on what your breaker is rated at, it won't trip until it's load rating is reached. Circuit breakers are designed to trip out as a result of dead shorts from major faults, as well as general overloading. They are by no means the answer for low current devices such heating pads and the like. Bear in mind, the filament in a torch bulb burns at over 1000 degrees C with tiny amounts of current and this as a reference, you can start a fire with half an amp that a circuit breaker will happily let through. This is why so many homes have burned down from electric blankets catching fire.
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Postby Rob » Fri Jul 20, 2007 9:02 am

Just back to the overloading of plugs. How much is too much if you have 1 socket with multiplug adapters and you're running heat cable and a couple globes?
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Postby froot » Fri Jul 20, 2007 10:56 am

Plug points are rated at 15 amps, but it also depends on the rating of the circuit breaker that the plug point runs from. That could be lower than 15 amps but you'll soon find out if it trips.
The best thing to do is calculate your load. Try and obtain the power ratings in watts of all the electrical devices in your setup, and other appliances you are running on the same plug point. Sometimes in winter you may be running a heater in your snake room. Add all these power ratings up and devide the answer by 220. You will now have the current draw on that plug point. I would say never let the current draw go above 70% of the rated capacity.

If you have a stack of multiplugs and adaptors on the plug point, it is not an issue as long as your caurrent draw is within acceptable levels and the connections in the plugs are decent.
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Postby froot » Fri Jul 20, 2007 11:29 am

Here's an example of my setup:

All the electrical devices in my snake room on 1 plug are:

Light bulbs:
15wx2=30w
60wx1=60w

Flourescents:
8wx15=120w
18wx8=144w

Heating pads:
15wx20=300w
25wx6=150w

Ceramic heaters:
100wx1=100w

Heating wire:
15wx4=60w

Oil radiator heater = 750w

The whole lot adds up to 1714 watts
Devided by 220Vac = 7.79 amps on that plug point, which is about half of the rated amperage on that plug so I'm not overloading.

Now for agruments sake lets take a setup with many high power devices and add them up. It may be possible that one of you could relate to a setup like this:

Light bulbs:
(infra red) 250wx8=2000w
(normal)60wx6=360w

Flourescents:
20wx15=300w

Heating pads:
15wx20=300w
25wx10=250w

Ceramic heaters:
100wx3=300w

Heating wire:
15wx10=150w

Now all this adds up to 3660watts
Devided by 220Vac = 16.64 amps
This is asking for trouble, you may get a decent tan in your snake room but something will start cooking and it may be the wiring in your house if the breaker doesn't trip.
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Postby Nivea » Fri Jul 20, 2007 4:12 pm

Froot, thank for the brakedown of how much power one plug can run. It has been a concern for awhile, so i have an extention running from another room so that i could be safe., but from the way you say to calculate, i am well safe.

Thanks
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Postby froot » Fri Jul 20, 2007 4:41 pm

Only a pleasure Nivea.

Here's a circuit I did for buffering thermostats, that is, installing a heavier duty relay on the output of a thermostat.

Image
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Postby wickets » Sat Jul 21, 2007 10:34 am

I just addad a 1A fuse in series with each of my heating pads. (Soldered into the wire and heatshrinked.) At a cost of about R2 per pad, it gives me cheap peace of mind.
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Postby Pythonodipsas » Sat Jul 21, 2007 10:54 am

This post was, and is such a good idea. It serves nicely as great guide.

Froot your drawing was at first a little difficult for me to understand, but i think i got it. I will probably pay for you to fly down and accomodate you just to help me set up my next snake rooms' electrics. :)

Wickets, your last post is a very nice, simple and effective method. Thinking out of the box!
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Postby froot » Sat Jul 21, 2007 4:27 pm

Pythonodipsas, funny enough I've been suggesting organising a roadtrip down there to give you a hand with electrics. It would be my pleasure.

A 250-300mA fuse would be even better. A 1Amp fuse would let 220Watts through to a heating pad that should only use up to 36Watts (I think thats the biggest one). Good point Wickets, simple in line fuses can only help.

Another thing you mentioned is heatshrink tubing, which I reckon is an excellent way to insulate, much better than insulation tape. For those that don't know, its a soft plastic tubing that you slide over a join in a wire and heat it slowly with a lighter. It will shrink over the join and provide 'good as new' insulation.
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Postby wickets » Mon Jul 23, 2007 9:16 am

For those that don't know


Sorry, having an electronics background, I just assumed everybody knew what I am talking about. :oops: :oops:
Froot, why I went for 1A, was to give my about 300% safety factor (no unnecessary blown fuses), while I knew the fuse was still going to blow in the event of a catastrophy.
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Postby froot » Mon Aug 27, 2007 9:01 pm

I drew up a circuit that's pretty easy to build that will protect your setup from rogue heating pads or wires.

Image

The fuse rating of 150mA will allow up to 33 watts of power to pass through, any more than that and it will blow. The circuit has 2 LED's (light emitting diodes), a red one that indicates a blown fuse as well as continuouity (and possibly a short) through the heating pad, and a green one that indicates power at the heating pad connections. If you ask at the shop for the components as they are on the sketch, they will know exactly what you want. The resistors are selected to allow 10mA through the LED's, you can try slightly lower values to increase the brightness. Too bright and the smoke escapes ;)
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Postby Bushviper » Tue Aug 28, 2007 6:30 am

Gee that is a pretty picture but it really means squat to me. Is there anyone here who would be interested in making these devices and making them available at a reasonable price?

If you have the time and inclination please drop me a line. I would also need one to run 5 of the large heating pads at a time if that is possible.
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Postby Long John Silver » Tue Aug 28, 2007 7:11 am

Would you guys consider globes to be safer than heating pads?
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Postby froot » Tue Aug 28, 2007 1:14 pm

BV if you want to run more than one heating pad off the same protection circuit, all you have to do is increase the fuse rating. You add up the wattages of all the heating pads you want to connect and devide the total by 220 to get the required amperage. You then round this up to the next available fuse rating that you can buy and get that. eg, your answer for arguments sake comes to 0.2385, you would get a 0.25A fuse = 250mA fuse. Using multiple heating pads does however compromise on the protectability of the circuit. First prize would be to use one circuit per heating pad.
If you want, I can throw some of these together for you.

Globes are safer from a short prevention point of view, but they draw more power to do the same job. Many people use globes in their setups and are happy, it also depends on what species you are keeping.
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Postby Bushviper » Tue Aug 28, 2007 7:00 pm

Thanks Froot, as soon as I get my new racks made up I will bother you for some of these safety devices.

Putting over 100 cages in one room is looking for trouble and I want to minimise any possible threats.
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