Is current through each "hot" leg of 240V half total?

[mattoak]

I searched through as many old threads as I could read and couldn't find this.

If I am running a 5500W 240V heater and want to control it with a SSR on one of the hot legs, does it have to be sized to handle the total current flowing to the heater, or is the current through each hot leg half the total current because it flows in both directions in each leg?

I want to know if I need to buy 25+A SSR's, or if a 15 or 20A will work. I have access to a couple of 20A.

Thanks

 

[mattoak]

I just did some outside searching and I'm pretty sure I answered it for myself....that current through each hot leg is the same as total current draw.
Can anyone confirm this?

 

[ivegot2legs]

I just did some outside searching and I'm pretty sure I answered it for myself....that current through each hot leg is the same as total current draw. Can anyone confirm this?

The current on each hot leg of a two- or three-pole system is equal to the total current. The current on each hot leg does not sum to reach the total current.

 

[heckels]

Hence, why when you use a 30amp 2pole breaker you need to run a heavier gauge wire and not two 14ga legs.

 

[kenh]

The current on each hot leg of a two- or three-pole system is equal to the total current. The current on each hot leg does not sum to reach the total current.

The current through a single phase 2 pole circuit is the same through both legs. This would be exactly like our 240V elements are wired.

The current through a single phase 3 wire circuit where the center is neutral and where you have 240V loads (heating element) & 120V loads (MARCH pump) is a little different.
The current is the same across both legs for the 240V loads - 22.9 Amps for a 5500 watt element.
The current is the same across both legs for the 120V loads - 1.4 Amps for the smaller March pump.
Where the wire is common the currents add together.
Assuming the 120V outlet your March pump is plugged into is wired across L1 and N:
L1 - 24.3 Amps (element + March pump current)
N - 1.4 Amps (March pump current)
L2 - 22.9 Amps (element current)

And for reference, the current through each leg of a 3 phase circuit is 2/3 of the total.

 

[The10mmKid]

I searched through as many old threads as I could read and couldn't find this.

If I am running a 5500W 240V heater and want to control it with a SSR on one of the hot legs, does it have to be sized to handle the total current flowing to the heater, or is the current through each hot leg half the total current because it flows in both directions in each leg?

I want to know if I need to buy 25+A SSR's, or if a 15 or 20A will work. I have access to a couple of 20A.

Thanks

You'll need those 25A+ SSR's

Make quality connections everywhere, as you'll have a lot of current flow and the opportunity to create heat at any poorly made junction. We use nickel plated terminals only. Crimped AND soldered for insurance.

'da Kid

 

[kal]

I'd recommend 40A SSRs. That's what I use with my 5500W elements as the 25A SSRs would be close to the rated limit, and 40A ones are not much more (only a dollar or two more).

Either way you need a heat sink too... Larger current capacity SSRs doesn't mean that you can use a smaller heat sink. The heat dissipated is the same.

Kal

P.S. Regarding the original question - current is a closed loop so it's the same everywhere in the loop.

 

[huntb]

You'll need those 25A+ SSR's

Make quality connections everywhere, as you'll have a lot of current flow and the opportunity to create heat at any poorly made junction. We use nickel plated terminals only. Crimped AND soldered for insurance.

'da Kid

And hopefully you solder after you crimp.

 

[crazyirishman34]

How do you solder a crimp connection with out melting the insulation on the crimp?

 

[The10mmKid]

Use non-insulated terminals.
Slide a piece of heat shrink tubing back over the wire before crimping on the terminal.

'da Kid

 

[crazyirishman34]

From my reading a properly crimped connection has the same omh load as a soldered connection.

 

[The10mmKid]

I'd agree with that statement.

Does the average handybrewer(my new word) have the tool to "properly" crimp a 30A terminal . . . very few I'd bet.

I hate using the ratchet crimper at work because it wont let go unless you've crimped the terminal tight enough. But we have now doubts about the integrity of the connection.

'da Kid

 

[crazyirishman34]

I agree that a ratchet crimper is needed to make a proper crimp. But you can buy a decent one for about $20. Not one that will hold up to constant use everyday but plenty useful for a hobbyist.

 

[ryan_george]

From my reading a properly crimped connection has the same omh load as a soldered connection.

This always seems to be a hot topic here. Yes, a properly crimped connector will perform flawlessly and will not require solder. Un-properly crimped connections could likely benefit from solder for additional mechanical bonding and surface area of the wire to the connector.

One could also argue that a crimped and soldered connection is worse than one without solder. Although likely not a problem for our control panels, soldered joints like this are a weak link in applications that experience a lot of vibration (ie. automotive). The point where the un-soldered wire meets the soldered/crimped region is a common spot for breakage due to fatigue.

 

[processhead]

How do you solder a crimp connection with out melting the insulation on the crimp?

It can be done with out melting the insulator, but requires good soldering technique.

The challenge is to do it quickly enough to not overheat the insulation while still allowing the solder to flow properly into the junction between the wire and the terminal. When done correctly, stranded wire will actually wick up the solder into the terminal.

And of course, uninsulated terminals are perfectly fine as well.

Crimped-only connectors are used all the time in industry. When done correctly they are probably as good as crimped/soldered connection.

For the hobbyist who just crimps an occasional terminal to a wire, soldering might also add a little added assurance of a low-resistance, durable connection.

My quick and dirty QA method is to crimp the connection, then tug hard on the wire and the connector to make sure the crimp is secure.

 

[crazyirishman34]

It just seams like a lot of extra work. I bought an OK ratchet crimper and did a pull test on the connection. It took over 50 pounds of pull to pull the wire out of the crimp. It most likely is more like 80# but my fish scale tops out at 50#.

 

[processhead]

A ratchet-type crimper should give a more fool proof connection since you have no choice but to keep pressing until it releases.

Other hand crimpers are only as good as the guy doing the squeezing.

 

[mattoak]

It can be done with out melting the insulator, but requires good soldering technique.

The challenge is to do it quickly enough to not overheat the insulation while still allowing the solder to flow properly into the junction between the wire and the terminal. When done correctly, stranded wire will actually wick up the solder into the terminal.

The hotter the better. The hotter you can get your soldering iron, the faster the immediate area will heat up and flow solder. If it is just above the melting temp of the solder, it will take a longer time to heat the surrounding area to that temperature and allow more heat transfer to the insulation.

 

[processhead]

The hotter the better. The hotter you can get your soldering iron, the faster the immediate area will heat up and flow solder. If it is just above the melting temp of the solder, it will take a longer time to heat the surrounding area to that temperature and allow more heat transfer to the insulation.

Exactly that.

 

[kenh]

And hopefully you solder after you crimp.

Crimp terminals are designed to not be soldered.