Unsafe Wiring Instructions

[Randall]

Whenever an old Fender or other amp comes to me for an AC cord upgrade, I routinely rewire the mains to the modern method of hot to fuse to switch to PT, and neutral to other side of PT.

[Helmholtz]

Actually no need for personal opinions here, as everything is regulated within national and international safety standards. In Europe this would be the Low Voltage Directive (being a law within Cenelec member countries) + the national implementations of EN/IEC 60065. In the US there are the relevant Nema and UL standards.
Everybody professionally manufacturing or repairing mains fed electrical equipment should be familiar with those. Otherwise he/she might get into serious legal trouble.

[Dave H]

Most guitar amps are quite clearly not 2-pronged appliances (small modelling amps run off a wall-wart being one exception), they are not double-insulated and therefore must be grounded. Grounded plugs can only be oriented one way.

I think H. was referring to the symmetrical European three wire plug which is reversible. The socket has two ground connections (at the top and bottom in the picture below)

[Reader]

And each of the two pins is hot just as would be the case for USA equipment running on 240VAC. In these cases, there is no "neutral" and DPST mains switches are utilized.

[g1]

In any case, I think mojo must be in some kind of violation of the codes, unless being a kit is somehow a loophole around the codes.
Like Randall stated in post #16, bringing old amps up to new standard is the proper thing to do. Just as we add 3 prong AC cords, we should move the fuses and switches into the hot line. And also correct the accessory socket wiring on those old Fenders that have them mis-wired.
Fender would not get away with the old style wiring today, nor would mojo is they were selling those kits as assembled amps. I don't know why they would not correct it for their kits, I'm sure people are constantly pointing out the error to them. All that I can think is they don't have a problem with 'period correct' taking priority over safety.
This is especially disturbing considering many people use their schematics even if they are not using their kits, and assume they must be up to date as they are modern construction. There are plenty of current DIY amps being built to incorrect standards because of this.

[minim]

I think H. was referring to the symmetrical European three wire plug which is reversible. The socket has two ground connections (at the top and bottom in the picture below)

[ATTACH=CONFIG]51635[/ATTACH]

Thanks for that, interesting.

[Enzo]

Well, this discussion isn't really about Mojo, but in their case. No, Mojo didn't do it "wrong" because they are a cabinet maker and don't know any better. They did it that way because the Fender amps they are cloning did it that way for years and years. And Fender did it that way because the two incoming wires each could go right to a lug on a component (switch or fuse holder), as opposed to a mid air splice or a terminal strip.

yes, we should always assume either side could be hot, but in general, we should wire things in the "proper" manner - fuse and switch both on "hot" side - with whatever other consideration we might have to insure safety in the reverse condition. (As in reverse wall outlet wiring)

[SoulFetish]

I agree that best practice is to use DPST power switches. My point in starting this thread though was to discuss the best wiring practice for amps in the USA that use the modern IEC Type B plug, run on the 120VAC single phase source and already have SPST power switches installed.

When I started building amps with the intention of selling them commercially, I read through the IEC standards for wiring and grounding audio/video equipment several times to insure I committed the relevant information to memory. I wanted to be certain I maintained compliance, and more importantly implement the most current safety practices in my builds. But, this was prior to working as a repair technician and was primarily concerned with new production equipment.
Does anyone have any information as to whether or not any accommodations or exemptions are made for older equipment and "grandfathers" them from having to comply with some modern requirements?
Also, I will keep barking up the tree to have a sticky article/thread which addresses proper grounding & mains wiring in modern and vintage equipment.

[Justin Thomas]

Does anyone have any information as to whether or not any accommodations or exemptions are made for older equipment and "grandfathers" them from having to comply with some modern requirements?

There are definitely specifics for each state/nation, but auffice it to say, when it comes to liability, if an amp develops aproblem that causes damage to property or life and it is determined to have last been in your hands as a tech/repair person & you failed to update the wiring, you may be "on the joook" for damages. This is why there are many among us who will not let an amp out of the shop witjout a minimum of having a 3-wire power cord conversion.

Justin

[drewl]

And what if the owner declines a 3 prong conversion?
Do you need to get it in writing?

What if you buy an appliance from a thrift store or garage sale and it causes a fire?

So many grey areas, and so many ways to sue in the land of lawsuits.

[Justin Thomas]

I've seen a lot of guys here say if the owner declines a three-wire conversion then they decline the work. I haven't had a customer decline one yet. Granted, only one I ever got was a 66 Princeton Reverb... They converted it.

Justin

[Pedro Vecino]

And what if the owner declines a 3 prong conversion?

"I... donīt... bargain"

[TimmyP1955]

We have some of what one might call semi-boutique amps of current manufacture that do not follow the 'fuse post first' rule. I have rewired some of them.