Isolation transformer and variac setup

For some time now I've had this isolation transformer and variac in storage.
Can't remember the spec on them but they're pretty hefty. Bought them as "old junk" ;D
After doing some research I'm thinking of hooking it up as follows:

Mains AC - fuse - on/off switch - isolation trafo - fuse - variac- Amp meter - Volt meter - fuse - outlet

This will be for DUT only, test equipment will be powered elsewhere with mains earth connected.

Does that hookup make sense?
There will be some tube amp tinkering, should I also put in a dimbulb somewhere?
I'm a bit concerned about inrush current. I've read about thermistors and time delay circuits. What do you do?
I'm thinking about finding an Ampere meter that reads 0-5 AC Amp, good choice?

Thanks in advance for any recommendations.

//Magnus

I have a variac under my bench that I've used for decades. In the US one leg of power is grounded, so the variac not being fully floating is not really a problem, as long as you only use it to feed product primary circuits that are isolated from human contact.

If you want to use the output AC voltage on the bench, then perhaps the extra isolation transformer seems useful, but if the voltages are high enough that isolation doesn't guarantee you won't get stung or worse.

JR

I do not see a need for *three* fuses.

Look-up the specs, figure what fuse is safe for the smaller of the two irons, put it at the input.

> should I also put in a dimbulb somewhere?

Lamp-limiter? An iso+variac rig begs for a (switchable) lamp limiter in many repair jobs.

You also want a lamp-limiter when you first power-up the iso+Variac rig! There are too many ways to wire these parts, and some of them are a dead-short on your wall-wires. Test lamp-limiter alone and with a toaster (heavy load), use it to flame-check the rest of your work.

And stock-up on INCANDESCENT lamps while you can. Small guitar amps, mixers, etc can use a 100 Watt lamp. Large Power amps may idle on a 100W lamp but a full-power fault may be hard to diagnose without a 150W-250W lamp. Of course a Fender-300 can't roar on a 250W lamp, but the lamp is only protection while fixing, not for serious playing/testing once fixed.

I will disagree about Variac "safety". I never trust "Neutral" to be where it is supposed to be. Even on outlets I wired myself. I have re-wired too many Hot/Neutral swapped outlets.

If the USA had the discipline that apparently the UK has, maybe we could expect "N" to be in the right place. OTOH any "N"on the German plugs is utterly un-determined.

5A AC passive meters have become scarcer. I found combo Amp+Volt LCD meters on Amazon at wow! prices, installed two in my home fusebox feeder, and have been very happy. The indications seem accurate, better than 2% for V and 5% for I. There are several, different ranges, with and without the current transformer (which you need). I think I got one very like this first one, but I'll give several to help you hunt around.

DROK Digital Current Voltage Multimeter AC 100-300V 100A Voltage Amperage Meter, AC Volt Amp Testing Gauge Power...    $12.99

http://ecx.images-amazon.com/images/I/61-e83mTJFL._SL1200_.jpg
http://ecx.images-amazon.com/images/I/51Q3KWOxU7L.jpg

RioRand 0-199.9V/0-20.0A DC VA Voltmeter Ammeter Volt Ampere Panel Meter LCD Dual Display Current Monitor Voltage...$22.90

Yosoo Volt Meter/DC Digital LED Amp Volt Meter Digital AC 300V 50A Blue LCD Dual Panel Volt Amp Combo Meter 110V... $16.98

These DO need boxes. They supposed to front-snap in a precise rectangle cut-out. I opted to rear-mount in a quasi-rect hole-hack, located with glued blocks and a paint-stick.

Make sure it is AC. If you are in 120V-town, make sure it says it will work on 120V (most are made for 230V-lands but some also display and light-up fine on 120V). I needed 100 Amps for whole-house, you surely want more like 10A-20A for better display of your likely currents. (Altho I have been pleased with the 100A display's readings in the 1.8A-3.9V range, my house's typical "idle" current.)

Apologies- anybody looking for whole-house V/A monitoring, the specific meters I got were off eBay, this:

http://www.ebay.com/itm/Digital-AC100-300V-BLUE-LCD-DISPLAY-PANEL-VOLT-AMP-meter-WITH-SPLIT-0-100A-CT-/121016413792



Shipping was indeed about 3 weeks to the US.

I used two because US power is 240V center-tapped and I was specifically interested in 120V loading. A 120V 10A microwave oven causes more light-dim than a 240V 20A clothes-dryer here, because my line is too long and my center-tap wire has non-negligible resistance.

Thanks guys!

My idea for this came from ham radio and guitar/amp forums plus I want to feel safer when probing with my scope.
I've seen one ham radio repair guy using two lamp- limiters in parallel to be switched in when needed,
easier to find lamps for something bigger (in series within circuit of course).

Good to know those Volt/Amp meters work ok, I've seen them on Ebay not knowing what to think about them.

I still haven't found out what to do about inrush current, nobody mention anything about that on those forums. Maybe I'm overthinking this... Anybody have an opinion?

//Magnus