Large Scale Central

? on amps, fuses, and LED lights

Hope this is the right place to get some answers… These ?'s are for a real full size steam locomotive, D&RGW 315…

1st some background, While undergoing our recent federal mandated 1472 inspection, It was noted that we have some issues with the lighting system. Apparently when restored in 2007 the wiring was a last minute issue, and was pieced together rather haphazardly. We have in the past 15 years had issues and problems, and now we can trace a number of these to the wiring issues. I opened a couple of junction boxes, and found wire nuts that were loose, and several that had come all the way off due to the vibrations of running, ( I have no idea who thought that you could use wire nuts on vibrating circuits)… I have taken on the project to re-wire the loco and bring it up to great current status.

Here is the spects.
Steam powered Turbine Generator. Just completed a $10,000 total re-wire and re-build. We really want to protect this generator.
Output 32VDC… 30 amps. My calc. says 960 watts max usage.

Headlight 250 Watts & Taillight 125 Watts These are Tungsten bulbs ( both on at the same time, front or rear dimmed) = 375 Watts.
Number Board 1 ea. 5 Watt LED =5 Watts
Class Lanterns 2 ea. 5 Watt LED = 10 Watts
Steam / Air Gages 1 ea. 3 Watt LED = 3 Watts
Water Sight Glasses 2 ea. 3 Watt LED = 6 Watts
Cab Light 1 ea. 3 Watt LED = 3 Watts
Engineers Order Light 1 ea. 3 Watt LED = 3 Watts
My calc says that we will be under 410 Watts Max usage. Way under the load limit.

The 32VDC 250 Watt Tungsten bulbs, are no longer made worldwide, we have a small stock, but are seeking LED replacements, but until we can source them we will
be running those. The rest of the bulbs are LED from the Marine industry and are currently really available, they are rated at 10 - 80 Vdc, 3000K. All sockets are E26.

When the Loco was restored, a not prototype “Fuse Box” was installed. inside are just 4 circuits each with a 30A slow blow Glass Fuse in a E26 receptacle. 2 of these circuits have 16 gage wire ( scary huh?)…

Here is what I’m proposing to do… PLEASE JUMP IN AND TELL ME I’M About to do something wrong, if you think I’m making an error…

I Will build a fuse box ( wood looking old ) and install a 30 Amp resettable breaker coming directly off the Generator to protect it from overload. I will install in the front of the box a AMP Gauge, and a Voltage Gauge, so we can tell exactly what is being used.
Headlight& Taillight, install 15 Amp resettable circuit breaker and use Copper Stranded 12 AGW wire.
All Other Circuits Individual 5 Amp resettable breakers and use Copper Stranded 14 AGW wire.

All connections will be crimped and/or soldered with waterproof Heat shrinked connectors.

PLEASE Give me any and all advise, I’m NOT and electrician, but I think I understand enough to make mistakes…

Dave T.


I have a friend who might be useful to you. I. Had offered a few months ago to set up a zoom chat for him to tell us about steam engine restoration.

Only one person expressed interest but was busy.

However, Jon may be useful to you. He is quite knowledgeable and well connected. Pretty sure he also understands the electrical stuff but can’t swear to it. If he doesn’t know, I am guessing he knows a guy.

If interested, DM me and I will reach out to Jon.

Otherwise, good luck!

Only question I would have is do they (The Feds) allow a wooden fuse box?

The Feds make no mention… When original built, 1895, they used open flame kerosene lanterns. In 1917 when she got the generator there were only two ( one for + and one for - ) carriage bolts thru the cab wall with wires bolted to them…

Various upgrades thru the years, I can see three different styles… and then the restoration mess in 2007…

I’m not an electrician, but like you I know enough to be dangerous.

Your calculations all look fine. If it were me, since you don’t need all 30 Amps from the gennie, I’d make the master fuse only about 5 amps over your anticipated full load. Maybe a 20A main breaker.

Have fun with this project!

EDIT to add: I’m with Rooster with concern over the wood fuse box. Why not use a standard sub panel box that will have all the mounts for your breakers and then just sheath it in wood? Much less of a fire hazard if anything shorts out inside the box.

Hi Dave,

It’s been a while since I’ve played in the design space but here’s some thoughts. Generally you’ve done pretty well. :grin:

I sketched up what I think you are planning, in single line form. Makes it a bit easier to follow. I split the headlight and tail light up, but that’s more to do with fault finding as you’ll loose both lights on a short circuit, and have to follow cables running to both ends of the loco to find the fault. No problem combining them if you want…

I put the voltmeter and ammeter after the main CB so they are protected if they fault (or a wire comes loose - much more likely).

I’ll second Jon’s suggestion to get a rated enclosure and cover it with wood. It’ll also have built in mounting rails for the rest of the kit. Main issue I see is that wood can burn, and if it does you might be kissing the $10k generator goodbye.

Be real careful of the wiring between the generator and the main CB. This bit is not electrically protected so double down on insulation and mechanical protection so it can’t melt or chafe through.

You’ll need to get DC circuit breakers (MCB’s). They’re a special manufacture and ‘normal’ AC MCB’s simply won’t work (either very well, or very long). DC just kills them. I’d opt for two poles per wiring circuit, again not like AC where there’s a common neutral (or negative) and you only need 1 pole MCB’s. But that’s my OCD…

I found some ‘RV’ MCB’s after a quick web search, seem ok for what you need. There’ll be equivalent ones in the US I’m picking. Note they only come in certain sizes, industrial ones have a bigger range but you’ll pay for that privilege. I put the size I’d use on the single line sketch.

Rooster is on the mark with his cable size size / voltage drop tables, but you’ll be fine with the cables you mentioned. I checked them running at 50 deg C over a 30’ run. Because I can… :grin: Voltage drop is in the order of 1.5V, only really applies to the headlight…

Well, rant off, hope this helps some.


A couple of things… The head light and tail light are both 250 Watt bulbs… But one is on full power, and the other is on < 1/2 power Dim, both are never on Full at the same time…

These are the circuit breaker I’m looking at using…

Will these work correctly?

I’d be real hesitant to say they’re going to work ‘correctly’. It’s what I mentioned above - it’ll be rated at 8A AC, and when they don’t mention a DC rating it means a high chance of failure after a few operations.


The reason is that AC turns itself off 120 times a second, so the contacts aren’t particularly stressed. DC never turns off so you have a mini arc welder each time it opens. Low cost material in the contacts simply doesn’t last. The worst case is they weld closed, and you never know until it’s too late.

There must be something similar to what I found on your side of the lake, those prices were NZD, incl freight so they must be around the $10 - $15 mark for you? Just need a weather proof version.

Gotcha on the head and tail lights. The load current current is 8A each on full, or 12A if combined with one on half power.

I’d use a 16A breaker if they’re combined, 12A breaker each for split circuits.

The curious thing about CB’s is they are actually there to protect the cable from burning up in a fault. So they need to be rated higher than the load to avoid nuisance tripping, and below the short circuit rating of the cable to keep the smoke in. Usually you go to the next size up from the maximum load…


Found what you were looking at on Amazon…

Are these the same type?

I do like what they bring to the table…

I’ll have to be careful as to the size of the breaker box, as location in the top front of the cab is very limited…

How many times do I have to tell you outdoor railroad types (including the 1:1 guys,) that the marine business has already solved most of those problems.
RV gear is fine, but isn’t rated for wet outdoor environments, like a garden RR or the cab of a steam engine.

My boat has a 6KW generator feeding AC to the AC systems, (e.g. water heater,) and to the battery chargers which keep the batteries powered for the DC systems - refrigerators, chartplotter, etc.

I have banks of AC and DC circuit breakers, and they are readily available from marine stores:

You’ll find DC circuit breakers, designed for hostile environments. My old boat had a DC panel with a Voltmeter and an Ammeter built in, plus a master circuit breaker. This one is similar but needs a master breaker.

@PeterT I went up to the Westmarine site to ck on some marine grade Breakers and boxes…

it seems that everything I found is “panel mount”, and the only box i found is to mount a surface mount panel into, and it wasn’t rated for DC…and way to large for the space we have…

So I may have been looking in the wrong place,…could you help direct me into the 32VDC area, please? No panel mount.

Dave T.

Good input Pete, marine hardware never occurred to me - solves the weatherproofing.

@Dave_Taylor, most of the ‘12V’ stuff has a voltage rating way more than that by default, so not much of an issue for 32V, but it pays to check the fine print.

It’s back to making sure it’s rated to break DC.


Pending what marine stuff you can find Dave, the combo of IP65 box and indoor MCB’s will work.

The MCB’s you linked are industrial spec (IEC60947) so are reasonably bulletproof, and seem to be a good product.


@Neil_Wiggins , Just curious , Where in NZ are you located?

I’m about half an hour north of Christchurch Dave, a town called Rangiora.

Ahaaaa The ULTRA Beautiful South Island… One of the few places I’d consider living at…

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Dave, as I have never had to build a boat electrical system from scratch, I had to use Google. “marine DC circuit breaker box” turned up several options, including this:
which says it is for 32VDC.

My current boat has a small circuit breaker box or two, but they are all euro as it is a french boat, or I would suggest them!

Shhhh, Dave. It’s supposed to be a secret… Don’t tell anyone hey? :wink:

Spent 1/2 a day at the really neat Arctic Training center and got to run around in the Snow cats…Fun. Also really wanted to climb the pole up to the Spitfire at the airport approach. Also My first experience in an all Electric City Bus… Wife and I want to go back and spend more time… The first 10 days wasn’t enough…

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