Boiler Burner Circuit Sizing

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kaveenkw123

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Hello Everyone,
Im working on a project where existing Oil burners are being replaced with natural gas burners for two Hot water boilers.

I did look into burners briefly to understand how it works but my understanding is regardless of all internal connections the burner itself is just a single point connection.
So i have the specs below, since its just single point power and the only major electrical component is the burner motor based on my research; is it right to get the MCA from NEC 430.250 based on the burner motor HP for circuit sizing?

Thankyou.
 

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One boiler horsepower is about 33479 Btu per hour

It was loosely based on the boilers ability to supply a steam engine. If you needed to run a 100HP steam engine, You needed a 100 Boiler HP boiler. And it's all based on 100 plus years ago efficiencies
 
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21 gallons of oil per hour is a big boiler. Two would do a big school.

The burner blower fan about 1.5 hp is about right. It's in that range. Most likely the gas train has external valves, on / off, and an emergency off, that get wired to the burner cabinet. Plus external controls, boiler operating aquastat, em high limit aquastat, plus a HeatTimer for the modulating fire control. Steam boiler has a different set of boiler controls.

It's a bit more than just bringing power to the burner. I've seen them done without the HeatTimer, but not ones that ran well.

All that stuff is field wired on a boiler that big. That's a knockdown. Comes in pieces and is field assembled.
 
Dunno, 75hp isn't that big a steam boiler. Depends on where "big" starts :LOL: . (Kind of like generators....)

I've seen multihundred HP boilers arrive completely assembled on a skid. From the few I've seen come in pieces, they were put together by boilermakers under the supervision of the manufacturer and the piece-to-piece control wiring was done by the mfg's rep. Different places will do it otherwise, of course.
 
zbang said:
Dunno, 75hp isn't that big a steam boiler. Depends on where "big" starts :LOL: . (Kind of like generators....)

I've seen multihundred HP boilers arrive completely assembled on a skid. From the few I've seen come in pieces, they were put together by boilermakers under the supervision of the manufacturer and the piece-to-piece control wiring was done by the mfg's rep. Different places will do it otherwise, of course.
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Cleaver Brook steel firetube type boiler would be one piece on iron skids. Could be mostly preassembed as far as on boiler controls.

The Smith at 21 gallons of oil per hour, Smith is a cast iron sectional. Could be 14 - 18 sections shipped as individual sections. Parts would come as a skid of cardboard boxes. That boiler the controls would show up in separate cardboard boxes.

The existing boiler with a burner change, that one could be mostly already assembled from the prior field assembly.

Still needs external gas train (external gas valves) wiring and a HeatTimer for the modulating fire.
 
zbang said:
To be fair, steam engine efficiencies haven't improved much in those 100 years.
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Actually I know little about the engine it's based on. All I know is it was reciprocating, no idea if it was condensing, or what type of valve gear, or if it was compound or not.

I probably should have picked a longer timeframe lol. This one ran until the late 1970's at (if I remember right) Youngstown Sheet & Tube


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I looked it up, the Smith 28HE says it's steam. 10 is probably the number of sections.

That's a different control set, pressuretrols and low water cutoff(s).

I've seen the modulating fire done with pressuretrols, but not successfully. A HeatTimer would be a typical safer bet. That's if you have to have steam and cannot go all hydronic.
 
zbang said:
Dunno, 75hp isn't that big a steam boiler
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I work on 4 Cleaver-Brooks steam boilers that are 500 HP each, Originally fired with heavy oil, now on natural gas and digester gas. My idea of a big boiler has changed quit a bit over the years. The bottled water plant here is supposed to have four 1,000 HP boilers on natural gas, but I personally haven't seen them
 
Joethemechanic said:
I work on 4 Cleaver-Brooks steam boilers that are 500 HP each, Originally fired with heavy oil, now on natural gas and digester gas. My idea of a big boiler has changed quit a bit over the years. The bottled water plant here is supposed to have four 1,000 HP boilers on natural gas, but I personally haven't seen them
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You bring back memories for me. I was responsible for a collection of Cleaver Brooks and Kewanee steam boilers in the 600-1000 boiler HP range many years ago. Back then, they were all heavy oil which had to be heated. On a good day we burned 10 to 15K gallons of oil. This location was only about a hour and half from you in the Media area (Delaware County).
 
texie said:
You bring back memories for me. I was responsible for a collection of Cleaver Brooks and Kewanee steam boilers in the 600-1000 boiler HP range many years ago. Back then, they were all heavy oil which had to be heated. On a good day we burned 10 to 15K gallons of oil. This location was only about a hour and half from you in the Media area (Delaware County).
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Here is what I see coming down the street when I get one of those calls in the night

326125191_1895534627462720_7483345697795980560_n.jpg\

That is where the digester gas goes when they mess up and the boilers go down. Digester gas seems to be more trouble than it's worth, but they have to burn it anyway. Not enough to even run one boiler though
 
This thread wins a prize for going so far off track. The OP is asking about a circuit for a 1.5HP 3phase 208v motor.
I'm sure everyone is suitably impressed with the extraneous info but I don't think he needs a lesson in Boiler HP & steam.
 
kaveenkw123 said:
Hello Everyone,
Im working on a project where existing Oil burners are being replaced with natural gas burners for two Hot water boilers.

I did look into burners briefly to understand how it works but my understanding is regardless of all internal connections the burner itself is just a single point connection.
So i have the specs below, since its just single point power and the only major electrical component is the burner motor based on my research; is it right to get the MCA from NEC 430.250 based on the burner motor HP for circuit sizing?

Thankyou.
Click to expand...
I've worked on so many projects like these, I size the based on 430.250. I never get MCA or MOP values for these types.

There's so many other connections that go into the controller...
 
I have wired many of those. With a 1 1/2 hp motor that is a power burner. Probably a Power Flame, Webster, Industrial Combustion etc. As pointed out by others there can be more wiring than a single point connection. Aquastats, low water cutoffs, pressure controls, feed pumps, gas valves gas pressure switches etc etc. You may have to wire emergency switches at each boiler room entrance for emergency shutdown.

Look at the specs and read the other sections, HVAC and controls etc. Others may be responsible for some of this work. You may have 3 phase to run for the motor and a seperate 120volt control circuit. Most burners fed with 3 phase now have a control circuit transformer in the burner control cabinet
 
Joethemechanic said:
Heavy oil or #2? I really don't see any heavy oil boilers around anymore. I don't think the refineries are even producing that much.
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Heavy oil is still around. When I started in 73 even a small elementary school could have had heavy oil. Usually #4. But your correct most of it has gone away. Hospitals and industrial accounts would still be using it although most of them would be on gas and #2oil by now. The pollution laws caught up with it
 
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