Connect 120 volt circuits to get 240 volts

AFAIK the usual safe way to do this is what I have--an aluminum plate with slots cut in it, bolted to the front of the panel so that the "generator in" breaker can only be closed when the main breaker is open.

It's a cheap and very slick solution to the transfer switch problem.

We tend to lose power about once a year, usually for less than a day. Late last winter we were out for 8 days. I got on the Con Edison outage page, and by extrapolating their progress during Day 1, I figured it would be about that long. There were no generators to be had by then, so I got one online, and had the electricians in to do the transfer switch and feed cable. (The generator goes outside, chained to a large Metasequoia.) I was up and running by Day 4, total cost $400 for a 4.4 kW generator and $1k for the electricians.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

It is two, god damn you gotta tell some people everything.

Only if you use it.

You never mentioned this earlier. If the box is locked, how can anyone turn on the electricity while you are working on it?

So the noise tells you electricity is available.

Understood. How about charging a capacitor bank at each stop between bus charges and use the charged capacitors to charge the bus. That would reduce peak demand. Mikek

So, if we hang a diode on each of the 480V 3 phase. We get 240V x (1 + .75 + .75) = 576V. Right? I think their design max out at 700V. Parts get more expensive beyond 700V.

Well the disconnect box is outside on the side of my house. There is a pad lock on it, but the lock is old, rusty and doesn't close anymore. It's mainly there for looks... it sorta looks locked.

Huh, no it tells me the generator is on. You seemed to suggest that I would forget it was on and then go blindly out and re-energize the AC.

Say If I did reconnect to to local AC power line would my generator then be trying to power the entire neighborhood? That would cause it to bog down quickly.

George H.

Right, I'm a cheapskate and wanted to avoid the ~$1k for transfer switch and electrician. Well the first time I did this I wasn't thinking about safety, just getting the furnace running to stay warm.

George H.

(Side note: after making my own double male three pronged plug I found that the previous owner had made one too. (found in the back of a drawer with other electronics bits.) I've always figured he did the same trick.)

unless they were all disconnected and then the risk is that you energize a line someone is working on

Which is exactly why generator transfer switches exist :)

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The British cheapskate way to do this (as in it meets the regs) is to simply plug your boiler in to a standard outlet mounted specifically for that purpose.

Then you can have a second outlet on a completely isolated circuit which is powered by the generator - or for super cheapskate, run an extension in when required.

Unplug boiler. Plug into temporary supply. Job done, safe, cheap, foolproof[1]

I can't see why that would fall too far foul of other jurisdictions - at least it is basically safe, idiot proof and easy.

[1] Apart from the slight matter of earthing/grounding which is going to be jurisdiction specific.

You made a Jesus Cord?

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I forgot to add - this is actually near zero extra cost for a new wiring job.

We require a double pole isolator to any boiler supply. A 13A unswitched socket meets the requirements. So the plug and socket replaces a double pole fused isolator of similar cost. Same backbox in wall etc :)

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No, you mentioned this earlier. If someone comes on the scene and doesn't know you are working on the wiring, he could simply open the switch box and turn on the power. You wouldn't necessarily know this had happened and still consider the wires are dead. In the worst case, you would soon be also.

Your generator is not the same frequency and phase as the AC power.

There would probably be a huge flash and the generator would be destroyed.

In all these discussions, it appears that no one has posted the tables showing the effects of electricity on the human body. For example, see

shock.html

human-body/

These articles generally agree that as little as 10 to 20 mA is sufficient to prevent someone from letting go of the wires. They are frozen until someone breaks the circuit.

Steve, I'm going to stop this discussion. The possibility that my neighbor is going to come over during a power outage, open up my connection box, turn on the switch, and then leave without telling me.... very small.

The exposed metal of the double male plug is more of a hazard. I'll agree with that.

George H.

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more likely to just trip the genny's breaker. I vaguely STR the deliberate parallelling of gens by connecting them directly together. IIRC the trick w as to connect them through a lightbulb, and when the f difference was low & the bulb went out, throw the switch to lock them in sync. Can't rely on th at memory though.

t

For some reason articles like that tend to focus more on worst case than ty pical outcomes. I had numerous shocks in my teens. I made a rough estimate several years ago from the available figures that around 1 in 600 shocks is fatal.

There's a big difference between what someone skilled might do in the lab & what is sensible to leave around where children or other clueless persons might encounter it.

NT

If you are using 480 V delta (with no neutral), better use ordinary 6 pulse rectifier with 6 diodes :-).

It appears that the 700 V they were talking about was after the boost PFC.

There are several ways of implementing a three phase PFC, one method is to use three independent single phase rectifier+PFC. The problem is that the DC from each unit are floating around. Mo big deal, if you still need DC/C conferrers, just use three separate DC/DC converters and just combine the final DC output. It appears this is what they are doing with three holes in the PCB for DC/DC converter transformers.

If they indeed used three independent PFC modules, each starts with a

4 diode bridge, so there would be 12 diodes total. Since the AC input to each single phase PFC module is taken between two mains phases, so no need for a neutral connection.

I did that on ships. There is a circular instrument called a synchroscope that rotates a pointer to show phase difference, and light bulbs to show voltage difference. You play with a steam valve and field until things line up, and then hit the paralleling breaker. Once they are paralleled, you let the governors take over. It's a little dramatic if you get it wrong.

I designed an electronic synchroscope once, a circle of LEDs and some PLLs and stuff.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

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That thing he's talking about is an interlock kit for which you will be rip ped off over $100. If your generator is powering a minimal load: furnace, r efrigeration, essential lighting, some kitchen receptacles for small applia nces and whatever else you can fit onto a 30A feed safely, then you use a M UCH cheaper 30 Amp transfer switch powering a subpanel containing your crit ical circuits. The transfer switch receives power through 30 Amp dual 240V breaker in your main panel and the generator. Obviously you want this insta lled near your main panel to simply moving the circuit cables around, you c an splice wires with wire nuts that remain in the main panel enclosure to g ive you some reach if necessary on the circuits that need moving from main to sub panel. And, if you match manufacturers, you can reuse the CBs from t he main panel in the subpanel, which will be a big savings. And things rema in cheap if you use all indoor rated components. If your generator is outsi de, then you install an outdoor receptacle, your only outdoor rated part, t o receive its plug, and run a 6ga from the receptacle to your interior tran sfer switch. You end up with a code compliant, perfectly safe and convenien t setup, so no headaches if you ever need the house inspected for some reas on.

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PFC.

The more I read about 3-phase power, the less I understand. But anyway, I'll just make use of other people's work. One suggestion is using

18 pulses phase shifting transformer instead of active PFC circuit. Disadvantage is the weight and size. Advantage is the simplicity and less semiconductor to go bad.

Sorry, I misinterpreted your earlier statement:

Apparently there are no 'helpful' individuals involved and you are alone working on the wiring. So I was wasing my time and concerns.