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Old 12-01-2011, 10:38 PM   #1
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Default Amp, gauge, duty cycle recommendations

I'm putting together a really simple boil kettle electric build. I'll build the PWM controller myself to regulate the element load. So I have a few questions:

1: Building the controller myself I can use just about any cycle length I want. I think most PID's use a 60hz cycle but I don't see that being necessary and rough on the SSR. I was thinking more like a second or so. So 50% would be .5sec on .5sec off.

2: This is going in my garage and I'd like the kettle to be stationed about 15ft from the breaker box. I was planning on running wire from the breaker down low in the wall space then through a conduit along the base of the wall then up to an outlet above the level of the kettle. What gauge wire do people recommend to run a 5500 watt element that far from the breaker? I was going to go with 8 gauge.

3: What size breaker should I use? I was thinking 40 amp.

4: What rating SSR should I use. I was thinking 50amp if possible to minimize heat.

Thanks

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Old 12-01-2011, 10:43 PM   #2
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5500w is ~23 amps at 240vac. You will want some headroom on the circuit as you only want to really pull about 80% max of the amperage load on the breaker or you will trip it often. 30A minimum for just the BK. 10 gauge wire is the minimum code requirement for 30A. If you put a 50A breaker on the panel, you need to run 8 gauge wire to the outlet on the wall. I would highly recommend just doing a 50A circuit with 8 gauge. I only did 30A with 10gauge to my garage and I already wish I had spent the money to just do a 50A from the beginning.

-Steve

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Old 12-01-2011, 10:44 PM   #3
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What voltage?

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Old 12-01-2011, 10:57 PM   #4
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Originally Posted by amb1935 View Post
What voltage?
240

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Originally Posted by sjwelna View Post
5500w is ~23 amps at 240vac. You will want some headroom on the circuit as you only want to really pull about 80% max of the amperage load on the breaker or you will trip it often. 30A minimum for just the BK. 10 gauge wire is the minimum code requirement for 30A. If you put a 50A breaker on the panel, you need to run 8 gauge wire to the outlet on the wall. I would highly recommend just doing a 50A circuit with 8 gauge. I only did 30A with 10gauge to my garage and I already wish I had spent the money to just do a 50A from the beginning.

-Steve
Good to know. Thanks

Another thing. 240v comes in 3 and 4 wire flavors. I'm assuming the element will only have 3 connections. Is that what I should be running to the outlet?
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Old 12-02-2011, 01:32 AM   #5
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240



Good to know. Thanks

Another thing. 240v comes in 3 and 4 wire flavors. I'm assuming the element will only have 3 connections. Is that what I should be running to the outlet?
Depends on what you want it to do.

3 Conductor - 2 Hot, Ground
4 Conductor - 2 Hot, 1 Neutral, Ground.

The three conductor is fine if you ONLY want 240V. If you want 120v also available in your control panel then run 4 conductor. For example if you want to also run a pump at 120V.
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Old 12-02-2011, 02:42 PM   #6
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usually the latch time for a SSR is 1-2 seconds. most PIDs dont let you set it lower than 2 seconds if i remember. you dont want the thing pulsing 25amps on and off several times a second. 1-2 seconds is good.

i agree with the rest of the suggestions. use 8 gauge wire, 50A breaker, and 40A or higher SSR with heatsink. the more you overprovision your SSR, the less it will heat up.

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Old 12-02-2011, 03:17 PM   #7
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Originally Posted by sjwelna View Post
5500w is ~23 amps at 240vac. You will want some headroom on the circuit as you only want to really pull about 80% max of the amperage load on the breaker or you will trip it often. 30A minimum for just the BK. 10 gauge wire is the minimum code requirement for 30A. If you put a 50A breaker on the panel, you need to run 8 gauge wire to the outlet on the wall. I would highly recommend just doing a 50A circuit with 8 gauge. I only did 30A with 10gauge to my garage and I already wish I had spent the money to just do a 50A from the beginning.

-Steve
8Gu is good for 40A so you'd need to move up to 6Gu wire to cover the 50A breaker. 6Gu should be good to 55A.
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Old 12-02-2011, 03:45 PM   #8
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Depends on what you want it to do.

3 Conductor - 2 Hot, Ground
4 Conductor - 2 Hot, 1 Neutral, Ground.

The three conductor is fine if you ONLY want 240V. If you want 120v also available in your control panel then run 4 conductor. For example if you want to also run a pump at 120V.
Is it compliant to tap a 120vac outlet from the 240vac circuit? Or does this split have to happen inside the appliance/control panel? Could the box at the end of the conduit have a 3 prong 240vac outlet and a 120vac outlet both derived from the 4 wire line? I could run a separate 120vac line from a separate breaker at the box but then the question is can this wire be housed in the same conduit as the 240vac wire? I do need both. 240vac for the bk element, 120vac ~20amp for an element in an hlt, and 120 (ultimately 12vdc) to power the controller.

My original plan was to run the two separate. Come out of the wall into a junction box with two conduits along the wall to a box at the end with both outlets. Obviously I'm trying to cut costs so if I can eliminate a conduit and put both lines in one, cool. If I can only run one and split it at the end into two outlets, even better.

BTW thanks for the help. I'm sure this comes up a lot but at least I'm not asking why my airlock isn't bubbling after 24 hours.
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Old 12-02-2011, 07:32 PM   #9
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It all depends on your supply. If your plugging into an old dryer outlet that has a 3 wire supply, then you will only have 240 to use. If you have a newer outlet, or are running directly from the panelboard, and have a 4 wire supply then you use the neutral to get your 120v.

If you have the 3wire, and need 120v the easiest option is to just use a second cord to connect to a 120v GFCI, just be sure to keep you circuits separate in your control panel.

About the SSR cycling too much and wearing out from 60hz, dont give it a second thought . Solid state has no mechanical parts to wear out. Heat is the biggest killer of SSR, so make sure your relay is rated for the load, and is properly cooled. (40 amps for the 5500 watt is sufficient)

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Old 12-02-2011, 08:45 PM   #10
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Is it compliant to tap a 120vac outlet from the 240vac circuit? Or does this split have to happen inside the appliance/control panel? Could the box at the end of the conduit have a 3 prong 240vac outlet and a 120vac outlet both derived from the 4 wire line? I could run a separate 120vac line from a separate breaker at the box but then the question is can this wire be housed in the same conduit as the 240vac wire? I do need both. 240vac for the bk element, 120vac ~20amp for an element in an hlt, and 120 (ultimately 12vdc) to power the controller.

My original plan was to run the two separate. Come out of the wall into a junction box with two conduits along the wall to a box at the end with both outlets. Obviously I'm trying to cut costs so if I can eliminate a conduit and put both lines in one, cool. If I can only run one and split it at the end into two outlets, even better.

BTW thanks for the help. I'm sure this comes up a lot but at least I'm not asking why my airlock isn't bubbling after 24 hours.

You're overthinking this. Buy the 50 amp spa panel from Home Depot, it comes with a gfci breaker 240v in it. This is the cheapest way to get a gfci breaker and it comes with a panel to boot.

Then put either a 50 amp or 30 amp breaker in your main box (I went with 50 but I have a 150 amp main so I had plenty of spare current - I don't anticipate running the water heater, range, dryer, and brewery at the same time).

Next, run some romex cord in a conduit to your spa panel, you want 4 wires, not 3 so you can have both 120 and 240v in your control panel..

Then install a 240v 4 wire outlet from (or in my case - 'on') the spa panel. Now you run a 4 wire range/stove plug from that outlet to your control panel. I went with a sturdy plastic tool box from lowes, it was $20. I prefer plastic to metal because drilling metal sucks as I found out when mounting the outlet on the actual spa panel itself.

Once inside the box you can split up the current as necessary but fuse it down first. At a local true value hardware store I found a terminal block with the fuse posts built right in. I ran one of the hot lines to this block and then ran all my 120v connections off of that (fused down appropriately). I used 14gauge wire to route the 120 around the box and used 8 gauge for the non fused stuff.

So one hot wire goes right to the switch, contactor, element or whatever. The other goes there as well but makes a pit stop first at the terminal block where you branch off your 120v stuff. I installed a 120v outlet into the side of the toolbox so I could plug in my HLT stirrer and my single pump. I also installed 2 240v 3wire outlets on the box so I could plug in my 2 elements. I wired my elements to some dryer cord (which is 3 wire, rated at 30 amp).. I then plug these into the outlets on my control panel when ready to brew and use a switch and contactor to switch between the element in the brew kettle and the element in the HLT (the switch switches between outlet 1 and outlet 2).


Note, the 5500w camco elements I and others are using cannot both be run simultaneously on a 50amp circuit, it's still 1 at a time. So you really don't gain much by going much by going 50amp over 30amp.. but I did because I could, it didn't cost much more, and it gives me more room for future expansion.

There's a really nice diagram by PJ here that I followed (minus 1 pump).
http://www.homebrewtalk.com/f170/sim...-1-pid-221403/

You can also get all the switches at lowes or radio shack. I didn't see a need for fancy lighted push buttons from automation direct when regular old bat switches work just fine. I would also suggest that you choose switches which require circular rather than rectangular holes since that makes installation a snap with a drill.
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