Steam generator manual question


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Old 01-14-09, 10:56 AM
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Steam generator manual question

Interesting thread, and timely for me.

Here's the doc for a steam generator I recently purchased:
http://www.steamist.com/Downloads/pdf2/228-F.pdf

Look at the table on the last page, I have model SM-8.

The way I read the table, they recommended at 240 volt I should expect it to draw 35 amps, and should use #8 romex protected by a 45 amp fuse/breaker. Is this recommendation not up to code or am I interpreting it wrong?
 
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Old 01-14-09, 11:37 AM
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Originally Posted by DarrenE
The way I read the table, they recommended at 240 volt I should expect it to draw 35 amps, and should use #8 romex protected by a 45 amp fuse/breaker. Is this recommendation not up to code or am I interpreting it wrong?
Technically the table they give is correct, however it is not legal to use that table for 99% of installations. The column label is "Wire Size 90°C", and the values they give for wire size are correct. However, most situations require a 75°C or 60°C wire rating which means you need #8 THHN copper conductors in conduit or #6 copper romex.
 
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Old 01-22-09, 09:03 PM
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I'm revisiting this again, still planning for the install.

The manual says "Only UL rated 90°C wire can be used". It also says "Unit must be wired with 90°C wire in a suitable raceway, or, if local codes allow, provide twist lock plug on a 90°C wire cord from generator to a 250v 2-pole, 3-wire grounding receptacle."

Is NM-B direct from panel to the generator not an option then? If not, and I want to use NM-B cable, should I do as suggested and use a twist lock plug? I found a manufacturer (Hubbell) that makes 240v 50AMP twist lock plugs and receptacles. It would have to be paired with a 90°C wire cord. I found an online source selling 600 volt, 6AWG cord rated at 90°C. Would a few feet of this paired with the Hubbell plugs and receptacles do the trick?
 
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Old 01-23-09, 05:25 AM
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NM-B is rated with 90 degree insulation. It cannot be used at the ampacity listed in the 90 degree column. That can only be used for derating purposes.

NM-B cannot be used with cord caps.
 
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Old 01-23-09, 09:03 AM
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Originally Posted by DarrenE
I found a manufacturer (Hubbell) that makes 240v 50AMP twist lock plugs and receptacles. It would have to be paired with a 90°C wire cord. I found an online source selling 600 volt, 6AWG cord rated at 90°C. Would a few feet of this paired with the Hubbell plugs and receptacles do the trick?
It would but when you price out 50A twist locks, a simple $10 non-fused 60A air conditioner disconnect with 6/2 NM-B cable will look very appealing.
 
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Old 01-23-09, 09:57 AM
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Thanks, I like the air conditioner disconnect option. Should I then use individual THHN wires in flexible metal conduit to go from the disconnect to the unit?
 
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Old 01-23-09, 11:24 AM
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You could do that, but if it's in an area which is not exposed to damage you can use a piece of #6/2 cable. The temp rating can be confusing. NM-B cable can be used in ambient temperatures up to 90°C, but for the purpose of determining the ampacity code requires us to use the 60°C rating. All wires heat up when current flows through them, so what the code is telling us is that you must design the circuit such that the wire temperature will not exceed 60°C as a result of the current flow. The temperature of the wire can however go up to 90°C as long as the heat source is external to the wire.
 
 

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