Are mains connections ok?

[Fay]

I was reading about it being unsafe to use  a mains connection for dew heaters  that are wrapped around the telescope.

Should we always use 12v batteries to power, the mount, laptop & camera's also? I use an extension cable with the mount, laptop & cameras plugged in, via transformers, when at home. I try to protect the plugs from the damp, but is this enough? The switches in the meter box, would trip, if anything untoward happened.

Fay

[Ian]

I would strongly recommend an RCD, you can get them in B+Q, screwfix and so on. I'm sure we've had this conversation before though...

[Mac]

Using the mains at home is perfectly safe within reason.

If you have a RCD device on your cable or main fuse box, this will protect you completly,

This will detect a difference of 20mA between the live and neutral cables and trip if there is a difference. thus protecting you.

The reason mains is so dangerous is because the neutral is connected to the earth at the substations.

So any fault path will try to return via earth, and normally blow the fuse.
so dont use a 13A fuse in a 1amp circuit, as it might not blow the fuse!

and as you are normally at earth potential, if you touch a faulty item,
i.e. a live dew heater, then you will complete the path and get a belt.

depending on what you are wearing, (shoes, socks, wet hands, ect) depends on the severity of the shock.

using an inverter is safer still as the 240v that is produced, is not referenced to earth.
i.e. the neutral is not connected to an earth point,

so if you are using an inverter to produce the 240v and you accidently touch the 240v, or a faulty item
then you will not get an electric shock, as there is no path to connect you back to the neutral.

[Mac]

forgot to add,
use an RCD anyway,
because if there is a problem it will always trip.
at home or in the field.

[Daniel]

I think I might have to invest in one of those, I use a mains connection for my dew heaters and laptop, some nights the extension lead I use is soaking wet by the end of the night.

[RobertM]

I'm always a bit concerned about having mains supplies around in the dewy wet conditions outside so I always use batteries now.  One is on charge whilst the other is in use then I swap them over every 1-2 weeks ( or every month or two if it's cloudy ).  The only thing that has mains power is the PC (protected with RCD) in the summer house which is connected to the mount through a single USB cable.  The battery also drives a dew heater.  If it was inside an observatory and waterproof then I would run mains cable straight to the mount and have everything main powered.

Whether it's in the observatory or not always use an RCD to power outside equipment, that is essential for safety's sake

[Ian]

using an inverter is safer still as the 240v that is produced, is not referenced to earth.
i.e. the neutral is not connected to an earth point,

so if you are using an inverter to produce the 240v and you accidently touch the 240v, or a faulty item
then you will not get an electric shock, as there is no path to connect you back to the neutral.

The same is true of isolating transformers, however it's still important to remember you can get a belt off of either of these things if you do complete the circuit. In the dark, in the wet, inverters and isolating transformers are not as safe as an RCD. Particularly if you don't use an RCD because you don't think something attached to a car battery could hurt you.

Regarding that, how about a welding demonstration at DSC using car batteries and a couple of sets of jump leads?

[Fay]

Ian, it has probably been mentioned before.
I read another articles about it & get a bit uptight again, wondering if I am doing things right.
I don't want to be the centre point of an explosion!

I will look for an RCD today, if I haven't already got one.

[Mike]

I've always used a mains extension in the garden. If it gets particularly dewey I will wrap it in a teatowel and put it inside a carrier bag.

[Fay]

Yes, I have to connect two extension cables together & I always put that in  a bag, as it sits on the grass.
My x4 anti surge adaptor, & all other cablesare on a piece of thick plastic, to keep it all off the grass.

[Mike]

Inside a bag with a packet of silica gel will keep it dry enough.

[The Thing]

I don't take 240v outside, I have a high current 12v supply (two laptop units) feeding a heavy gauge 12v garden lighting cable terminated in a 4 way car socket with a hardwired feed for the scope power. This powers dewheaters and air blowers if needed. I can run a laptop off it as well using a car converter 12 -> 19v if I have too. The laptops (an old one for dslr image capture - driver issues) usually sit in the conservatory with active USB and serial cables running to the scope, much more comfy and closer to the kettle.

[MarkS]

I run everything off a 12v battery - including laptap.  Just like Duncan I use a 12v to 19v converter - the 19v can be changed to other common laptop voltages.