Layout Power Calculation

[WHartman]

How can I estimate the amount of electrical capacity I'll need for my soon- to- begin layout? It will be n-scale, DCC, and approximately 25' by 15 '. Large yard and perhaps a dozen locomotives operating at once. Is there some sort of rule of thumb calculation? I'll need the info to give to my electrician so that he can properly prepare the room prior to benchwork construction.

[selector]

The large area is not so much a problem from the point of view of power, but in the wiring to get the power to the large area without losing voltage over long lines. So, you use a solid bus of 12-14 guage wire, and then drop feeders in the 18-22 guage range to your rails. To minimize the deleterious effects of shorts, inevitable as they are from time-to-time, you should gap your rails into 3-6' sections that are each fed by one set of feeders. As Joe Fugate recommends, wire a 12 volt tailight bulb in series into each feeder set; the bulb will light up when the short occurs at the rail and act as a buffer to save your loco from having its decoder fry.

I am most familiar with HO, and the general rule is that you can run four locos on 2 amps unless they have QSI sound decoders. Some other makes take less power, but 2amps would limit your road to about three QSI-equipped locos, in which case that level of amperage draw would make the taillights essential. In N scale, with sound, 12 locos will need about 5-6 amps as a minimum...and that would be on the razor's edge.

N scale, if I have it right, uses lower voltages, so the amperage draws are potentially lethal for locos with decoders if a short occurs. Please heed the advice to wire in the short protection.

By the way, I take it you will have other cabs/throttles with guest operators with that many locos...or are you running them with a computer?

[dgwinup]

I don't remember the power draw of locomotives, but your power supply (DC or DCC) will have ratings on them. Add up all the ratings to get your total power requirement.

If I had to estimate, I would estimate 1 amp per engine, or in your case, 12 amps (for 12 locos). All your other accessories will draw no more than that, so a safe estimate for total draw would be around 24 amps. This will help your electrician determine your needs.

I would recommend that your electrician install 'kitchen circuitry'. Code requirements for kitchens are two small appliance circuits of 20 amps each, plus an additional circuit of 15 to 20 amps for lighting. If you are in a basement, the outlets should be protected by Ground Fault Circuitry (preferably AT the circuit breaker!). If you don't have circuit breakers, the electrician can install GFCI outlets, one on each feed, to protect all the outlets on each circuit. CAUTION: Talk with your electrician! You do not want a multi-wire installation for your outlets. They can not be protected by GFCI at the breaker box. Multi-wire is approved under code requirements, but is no longer a recommended practice, and good electricians won't install them.

After the installation, make sure you know which outlets are on each circuit. Suggestion: have the electrician run different color outlets for each circuit. Make sure you keep the power usage below the ratings of each circuit (20 amps). Just because a plug is available doesn't mean it can be used safely. You could wind up with too much power draw on one circuit, creating an electrical hazard and making your operations difficult if you constantly have to re-set tripped circuit breakers.

These recommendations should give you plenty of power for your entire layout, accessories and lighting, and keep your layout safe for your enjoyment.

Hope this is what you needed.

Darrell, quiet...for now

[rrinker]

A typical N scale loco draws around .25-.5 amps per loco, newer ones probably a lot less (since I have some HO locos that are less than that). Physical size of the layout really has little to do with power requiresments - it's how many locos you plan on running at the same time, and anything else that draws track power - such as lighted passenger cars. An 80x100 layout with three locos running needs a lot less power than a 4x8 with 12 running.
A critical thing, especially on alarger layout, is distribuing the power to keep the track power bus wires as short as practical - on said 80x100 layout you wouldn;t want to put all the DCC boosters in one corner. 20 feet of wire isn't a problem. 100+ is, even with heavy wire that is not easy to work with.
You would also want to think about dividing the layout into power districts using electronic circuit breakers or light bulbs. You might calculate your power needs to be no more than 5 amps, which is one typical booster. But bu adding the breakers to make power districts, you gain the advantage of one operator derailing and shorting in the yard not stopping every other train running. Trains just stopping can be just annoying, or it can make a mess - a long train on a downhill curve that just stops suddenly might throw the cars all over the place. Or if not when it stops, when it suddenly takes off when the culprit fixes his problem. Power districts avoid this and keep things moving for everyone else.

--Randy

[WHartman]

Thanks for the advice! The power districts are an excellent thought.

[grayfox1119]

From your question, you are asking what to tell the electrician, which means that you are looking for number of circuits and how many are to be 20 amp general purpose and how many for lighting. Each 20 amp house circuit uses #12 gauge wire and is rated at 2400 watts max. Electrical code using a de-rating factor of 20% for safety, so that means 1920 watts per 20 amp circuit. That would mean a safe draw of 16 amps. One circuit could handle your layout just fine. However, I would add a second for your workbench area, which will have soldering iron/s, a few tools, fan, etc. Then one 15 amp lighting circuit on #14 gauge wire will be sufficient for any lighting that you will ever need on a layout that size.
As mentioned already, all garage, basement, exterior, or wet locations MUST have GCFI protection. This can be in the form of a GCFI circuit breaker in the manin panel, or panel feeding your new line, or, a GCFI outlet, which is placed first in the line, so that all following outlets are protected. You must make sure that you wire the GCFI properly to give GCFI protection, follow the directions given in each box containing a GCFI.

[Leon Silverman]

Previous replies to this post have suggested that you can power your layout with one 20 amp circuit and use a separate circuit for your workbench and lighting, for a total of three circuits minimum.
You did not state what your environmental conditions are. If you will need electrical power to provide heat or AC, these should be separate additional 20 amp circuits.

[grayfox1119]

You mentioned 25 X15 sized room, so unless you have half your living level available for a layout, I assumed that you were in the basement. As such, it is extremely rare to need AC in a basement. Dehumidifiers? Yes indeed, in the humid Summers. And if you don't have heat in the basement ( most homes do have a furnace in the basement), then you will need to factor that in also for additional circuits, like for electric heaters, or another zone off your forced hot water, or gas heat furnace. Please give more info so that we can give you more accurate data.