Power load requirements

[Leigh]

If you install two 20-amp lines, fed from opposite sides of the breaker panel, then you'll have 240 volts available if you ever need it.

- Leigh

[Drew Wiley]

If you're just going to do basic black and white printing you'll be fine. But if you decide to get into color you'll probably need more juice. I'm referring just to processing. Things like room heaters or high-efficiency fans and dehumidifiers can significantly add to the equation. If you are wiring new, it's just common sense to
have a surplus.

[resummerfield]

In addition to the three 120V circuits, consider one 240V 20A circuit. You might acquire something in the future that needs the higher voltage.

[polyglot]

If you're just going to do basic black and white printing you'll be fine. But if you decide to get into color you'll probably need more juice. I'm referring just to processing. Things like room heaters or high-efficiency fans and dehumidifiers can significantly add to the equation. If you are wiring new, it's just common sense to
have a surplus.

Or you just use a Jobo or Nova. No particularly huge power requirements there.

[Larry Gebhardt]

I would run 20A lines as well. I have a few things that draw over 15A, such as the NuArc for alternative printing. It's also safer not to right at the edge of the wiring rating, so 20A gives you a bit of a safety margin. I use 12gauge wire for all new power circuits, even though 14gauge is code for a 15A circuit. I still use 14 gauge for lighting circuits that I know won't ever see much load.

[koh303]

Or you just use a Jobo or Nova. No particularly huge power requirements there.

My two cents:
Just remember that when the Jobo thermostat kicks in the power requirement can momentarily spike to up to twice the stated max on the label, which can cause breakers to pop if they are too sensitive (or old).

[polyglot]

My two cents:
Just remember that when the Jobo thermostat kicks in the power requirement can momentarily spike to up to twice the stated max on the label, which can cause breakers to pop if they are too sensitive (or old).

Are you sure about that? The heating element is purely resistive and should have no appreciable inrush current. On my (240V) Jobo, the element resistance is 60 ohms for 960W nominal. The panel says 1050W. I'm not seeing how it's going to suddenly pull 2kW - that would likely blow the Jobo's primary (6.3A fast) fuse in pretty short order.

The motor reversals will cause current spikes, but not anywhere near the scale of the element power. More like 100W at most I would expect.

[Allen in Montreal]

Thank you for all the tips.

Good point about 20g wire, I would have defaulted to 14 as almost all the breakers in the house are 15a.
But I might as well upgrade up to 20a while I am there.

The darkroom is heated by hot water pipes that run thru the room the entire length. I have not spent a winter in the house yet, but given the past owner had his tool bench there and never seemed to complain, I assuming it will be warm enough. But that was the idea behind the third line, just as backup/future needs for a heater or other.
The lights are on a separate breaker with 2 other lights in the basement.

[Drew Wiley]

Just like kitchen appliances, things can add up pretty fast. If you don't want to be limited in the future, plan appropriately. Just a fan on a pro color enlarger might
draw a lot a current, not to mention the light wattage. Maybe you want an instant hot water device - lots of wattage there. Air conditioning, or a serious fan that
will efficiently circulate air even when it's rainy or humid outside? ... and if you're on the edge, some devices might not operate right at all. Again, no different than
wiring a modern kitchen where the building codes call for a hecka lot heavier wiring than in grandma's day (including 220). Just depends how flexible you want to be
in the future, and what your current budget is. But if you're remodeling a space anyway, a little extra wiring in the initial phase of the process isn't all that much
extra. It would be a lot more expensive to retrofit later on.

[Steve Goldstein]

Others have mentioned the possibility of a small fridge, but you might also find you want a microwave in there for drying test prints like Ansel did. That's another 1500W-2000W. All the more reason to go with 20A services.