Quote from: wattMaster on August 07, 2016, 01:03:02 PM

I would use to two 120 Volt outlets, but then how to we turn them on without cycling from the voltage surges?

When the lamps are still cold, they have pretty low arc voltage, so are inherently way more robust against these surges. In that state the lamps are capable of immediate restrike, even before the electrodes cool down again, so although it may flicker few seconds, it will settle and start after that.
The problem is when the lamps warm up, then there is not much margin. Plus once it get extinguished, it is not able to reignite immediately, so it means another cool down/ignition cycle.
So how to power them?

So how to use the thing:
Because even an apparently low load (even a 100W notebook power adapter) could have quite high inrush currents, it is not any good idea to power anything else from that generator than the two lights.
Then just wire them without any switch or so, connect them when the engine is still stopped and then power them ON/OFF by just starting/killing the engine. That will ensure all the transients happen when the lamps are still cold and so capable to restrike immediately. Since the lamps start, nothing will change abruptly in the system, so unless it becomes really unstable, it will light steadily till the gas runs out.
And that is the reason, why I said the fixtures should have no switches: My experience with such outdoor mobile installations is, sooner or later someone will accidentally touch some of the switches and that will extinguish the lamps. Having no switches means this problem becomes eliminated...

Now I know one of the reasons my electronic MH/HPS ballast has no switch. And you couldn't plug more things into it anyway because both of the 120 Volt outlets would be taken, and not many things need a 240 Volt 20 Amp outlet, but if you needed it, you would likely be in a situation where a pre-made engine powered dedicated flood light would be used.
You wouldn't want to use power strip because of resistance and losses.
What's a good wire gauge to use for connecting the plug and ballasts? The distance would probably be 25 Feet (~7.6 Meters).

Just the appropriate size to reach the current rating, not different from any usual installations.
The wiring resistance there will be negligible, mainly compare to the output impedance of the generator itself. So in that matter it will be even more tolerant than the real mains...

Here for cables on free air (just all the flex cords and so on) 2.5mm^2 should be sufficient for up to 25A.
When enclosed in conduits (so worse cooling), a 4mm^2 gauge should be used.
The good thing is, you do not need that much margin for a short circuit thermal load, as unlike the real mains, the generator will be quite limited in the short circuit current, so it won't pose that stress on the wiring.
But check this with your local code and mainly the cable ratings.
But I would not overdesign the wiring, as the cables will be quite significant part of the total weight of the complete thing (I guess we are talking about a kind of selfcontained mobile lighting tower or so)

I suppose 10 AWG would be fine for this.

I suppose 10 AWG would be fine for this.

I don't know what your Code says, but the AWG10 (= about 5mm^2) sounds to me like quite heavy. According to this, AWG14 cable should be still sufficient (assume free air or freely lying on the ground)

According to this conversion table, an equivalent (Read: the nearest thicker) to the 2.5mm^2 I would use here would be AWG12 (~3.3mm^2). The voltage drop over the 25 feet (~15m round) would then be less than 2V for the 20A current, what I think is good enough for the task (the generator impedance drop will be in the 10V range or so).

2.5mm2 for 25A is over the top. Under best conditions it is marginal at best. And thats before we mention some of the "2.5" "Copper" cables present on the market

Well, they would be enclosed in something to protect them from any items that may cut the cord, and once that happeneds, sparks start flying.
I was thinking of some kind of double insulated cable, the kind you usually find on big extension cords.

That is the only thing really acceptable for flexible low voltage power wiring. The "lamp cords" sorta things are too easily damaged, so can be used only in places where everything is accurate and static. For anything that moves, or even just for static stuff if your house is not exactly a "very ordered house", then "lamp cords" are an absolute no

Also, the double (or some triple) isolated cables vary - Some are more damage resistant than others. Atleast here the cables of different purposes have different colors, the one used on heavy duty extension cables and such is usually Orange (i use the ordinary White stuff, but i pick the best quality one, which is no worse than the Orange stuff from the average cheap import manufacturer)

That is the only thing really acceptable for flexible low voltage power wiring. The "lamp cords" sorta things are too easily damaged, so can be used only in places where everything is accurate and static. For anything that moves, or even just for static stuff if your house is not exactly a "very ordered house", then "lamp cords" are an absolute no

Also, the double (or some triple) isolated cables vary - Some are more damage resistant than others. Atleast here the cables of different purposes have different colors, the one used on heavy duty extension cables and such is usually Orange (i use the ordinary White stuff, but i pick the best quality one, which is no worse than the Orange stuff from the average cheap import manufacturer)

It won't be lamp cord thin.

I am not about the conductor section, but about the isolation thickness and construction. Electrically, even the lamp cord can handle several 100's V no problem continuously, and couple kV impulse. But mechanically the single isolation type is inappropriate where the cable is not treated "nicely"

I am not about the conductor section, but about the isolation thickness and construction. Electrically, even the lamp cord can handle several 100's V no problem continuously, and couple kV impulse. But mechanically the single isolation type is inappropriate where the cable is not treated "nicely"

Then what's a good kind of insulation/cable to use for this?

Ordinary double isolation - if relatively thick - is fair enough if you dont abuse it. If you abuse it there are other types of cable for that, but those would probably be called/rated in quite different ways in the US and here

And regardless of the type of cable, inspect it sometimes before use to see that it had not cut or got damaged somewhere along its length

Where would be a good place to acquire this cable?

I guess electrical wholesalers, as the main users for those rough service cables are industrial users. But first, do your research and find out which cables exactly are available and what use condtions are they intended for, according to codes and practices in the US, and not to words of the sales personnel at the wholesaler

2.5mm2 for 25A is over the top. Under best conditions it is marginal at best. And thats before we mention some of the "2.5" "Copper" cables present on the market

For cable lying freely of just in a single layer on a drum the 2.5mm^2 is rated at more than 30A.
The sizing you are talking about is valid when the cable is within a conduit or in at least three layers on the drum, that is where is the 19A rating.
All above means 60degC ambient (so max 70degC core temperature) rated insulation and default 30degC ambient.

The AWG12 has 3.3mm^2, so from the previous it means either 25A instead of 19A, or for the 20A it means ambient temperature of ~40degC in the conduit/in 3 layers on the drum. The corresponding "single layer" rating would then be above 55degC for the 20A (again, recalculated for the same 70degC core temperature).

Of course, pushing the cable to the limit is not that good idea, but I doubt there will be anything close to the 55degC ambient limit when the lights are running (I doubt anyone will ever start them at noon time for anything longer than just a few minute test and at the evening the sun won't create that much heat), I don't think it will ever operate above 40degC (so core barely at 55degC). And that should give enough margin...
And way more margin you get from a 105degC rated cable of the same cross section.

But the AWG10 has about the same margin as the 105degC rated cable, but it will be way heavier to handle and way more expensive to buy.
It is really question of how the thing is supposed to be arranged:
If it will be on some tower-like stand, definitely the lighter cable with higher temperature rating would be more suitable.
If the things are just rather low mounted lamps, but with long cable lying on the ground, the heavier cable may offer a bit better strength (larger radius around the conductors usually means it need larger forces to really damage the insulation).

And when just a single cable is in a conduit, the derating factor towards free-air is 1.0, that means if you cover single cable by some protection tube, the current and temperature limits remain the same. For two cables inside a single tube it means the maximum temperature for the standard (=60degC ambient/70degC core rated) cable would become 45degC, so even marginal, it should be OK.

All data coming from the same datasheet as mentioned before (it lists just the "60degC" type cables, the higher temperature ones just bring higher temperature margin)

What happens at the connections ?

Not all types of connectors provide lot of contact area. In some it is big (wire nuts, wire under pressure plate or screw head), in some others it is quite marginal (Eurostrip terminals), or even tiny (Wagos). In the latter, the connection might be bigger problem than the uniform wire even if done apparently properly. Thicker wire means mostly bigger connection surface, and also better heat conductivity to transfer heat away from the connection and spread it along longer part of the wire

And what about the wire specification ?

For example, what if the standard requires 2.5mm^2 +/- 10%, but the manufactrers make it 2.27 +/- 1% (just example) ? They would obviously get away with it according to standards, but would we get away with 25A on such cable ? Finally, with some cables i seen on the market lately (all imported from the same overseas place) i'd suspect whether they are even compliant at all, but not allways there is choice what to buy