How to wire up a torodial transformer and power switch?

[harry]

Hey guys,

i've almost built some 1176's and various eq's but -
this might sound silly - but i cant seem to find a clear explanation of how to correctly wire a power switch (on / off) and torroid transformer on the net.

I'm assuming there is a lack of explanations online due to liability stuff?

anyway - as far as the switch is concerned - i've got some dp switches - do i switch the 'hot' only or both the 'hot' and 'neutral'?

i'm using a lorlin mains rated rotary (has four terminals on it - the switch breaks or makes the two pairs)

i've read that it is dangerous to only wire the 'hot' to the switch - but i've seen this on most bits of gear i own.

i've also read that wiring both the 'hot' and 'netral' to the switch is also dangerous - i'm guessing because of the proximity of both wires on the switch - might arc?

i would use heatshrink over the bare wires (2 layers is what i have read is the go)

also as far as the torodial - the chassis cant touch the bolt at both ends right?

i feel like and idiot - all my stuff worked perfectly 1st time (as tested with a bench supply) but i can't feel 100% sure about this power stuff as i'm yet to find a clear 'definitive' explanation

harry arvanitis

[rick]

ok harry
if you dont understand dont do it - its a simple as that
get some local guy to give you a hand .. pickstone etc

[Ben M]

Harry I'm right there with you. We must be living parrallel lives.

I've got my 1176 clone ready for power, the torroidal is sitting ready for connection. I also have 2 Neve clone boards I'm building up and that will soon be the same problem. POWER?

Last thing I want is to fry myself because of some silly mistake with the power connection.

Not sure? Maybe I'll have a chat with my local electrician.

cheers

[Milo]

Don't chat with your local electrician! They're a different breed to an electronics tech.
I've just received an amp from a customer, where the electrician on the install found a mains cable and a speaker cable in the roof, thought they were the same thing, and joined them together. Result: a $3,500 amp written off because of 240 volts stuck into its speaker output.
I've had an electrician last week bring a mixer in which wasn't powering up. I asked him did he check the mains fuse (that's all it was - caused by a power surge). he wasn't sure how to do that.
I agree with Rick: mains wiring may be simple, but you've got to be confident with it, especially things like putting the fuse in the correct place in the circuit, for example: fundamental imortance.
Get some help.

[harry]

Good point Rick - i do know how to do it (almost)
it's just that i have had seen 2 conflicting examples of how to do it (switch the hot only) or (switch hot and neutral) and i want a definitive concrete answer:

ie:
A - wire the hot to spst switch only
B - wire hot and neutral to dpst switch only
C - either way is okay

as for the fuse - the holder is built into the iec socket and the correct fuse rating is written on the transformer box..

i hit wiki and started digging - still couldnt find a definitive answer in regards to this...

found this on a repairmans site:

this example is how i assumed i'd do it (following the guidelines in the text -plastic sleeves over contacts, cables firmly held in place ect)

http://sound.westhost.com/psw-f2.png
so yeah sorry for asking in my vague convoluted way of doing it...
hope this post is clearer?

harry arvanitis

[Milo]

The website wiring is correct. Connecting the neutral through the switch or straight to the transformer will make no difference, unless you have two fuses in the fuseholder - one for the active, another for the neutral. Connect it where its most secure and protected.

[rob]

as a rule of thumb, just wire the Active to the switch.
Less chance of error and less chance of a mains short should the switch break down inside

see my article in AT issue 63...the sidebar titled "I built it myself", this discusses a couple of important points.

http://www.proharmonic.com/articles.htm

If you aren't super clear on how to wire this and also understand how to make and test for a chassis to mains earth connection, I'd recommend you get a tech to do this.

Also you are keeping in mind that if you in any way use this equipment commercially, including recording a mates band and they sling you a $100 you must have this equipment tested and tagged?

[harry]

Thanks Rob,

that was the explanation i was looking for - 'just switch the active'

I'm assuming checking case earth continuity is just making sure that the chassis earth is connected to the earth prong thereby earthing all the metalwork (which would shunt voltage if it made its way to the metalwork)

Now i've got to read up a bit more about why the torrodial bolt must only touch the case at one end....

And find someone in melbourne that can look over my racks and say 'yep all good' before i switch em on..


Harry Arvanitis

[rob]

oh yeah...good point about about the torodial...don't let the other side of the bolt even look like it might touch the chassis, or you'll be building an arc welder.

You need to check that the earth pin of you IEC socket meters to less than 1ohm on the chassis.

[Mac]

don't let the other side of the bolt even look like it might touch the chassis, or you'll be building an arc welder.

LOL.. ..I like that!

Hey Rob, can you explain a bit more about the 1 ohm measurement? Why 1 ohm?

[no-fi]

the metal chassis needs to have a solid safety earth connection in case something happens and mains active ends up touching it. In this case it has to be able to put away a lot of current without burning out and leaving the chassis live.

At the company I work for I'm doing some of the electrical safety stuff for a new product, and from what I can tell of as60335 as it relates to our product, we've got to measure 0.1R given a 25A fault current. I got all my bits setup today for measuring the prototype tomorrow. including a 0.2 ohm 160W resistor made of 16x 3.3 ohm 10W resistors in parallel, nailed to a piece of wood....... hope I don't burn too much expensive stuff... :-)

[rob]

Australian / New Zealand standard 3760/2003 which relates to electrical safety testing says that the maximum resistance in a bonded earth ie from a metal chassis to the mains earth pin should be less than 1ohm

[Chinagraf]

Unless you have a sparky's ticket get a tech to do any mains work. It's not like teaching yourself to engineer, where if you mess up you only end up with a bad mix....

[Mac]

Australian / New Zealand standard 3760/2003 which relates to electrical safety testing says that the maximum resistance in a bonded earth ie from a metal chassis to the mains earth pin should be less than 1ohm

Ah thanks...just wondered if the "1" was a magical number you had calculated as a benchmark from years of experience or just a generic figure. Statutory figure = almost generic!