noob electrical q about timer box and amperage

[apartmentblower]

hi

i need to put in a new 240v circuit to run my new room. im learning up on it before i do it. but the little things have me confused...

heres one:


i bought an "Intermatic T104" timer board, which is already wired up to the needed 240v outlets, so thats taken care of. I just need to hardwire it to my new 240v circuit when i drop it in. What I'm confused about is, do I absolutely need to run this on a 40amp circuit? I got a bit confused, and I thought the guy at the hydro store told me to buy a double pole 30amp 240v breaker. I'm only pulling 10 amps + fans on 240v so 30amps is fine for that application, but why wouldn't he tell me to put in a 40amp circuit and breaker instead? Maybe I got confused and he really did say 40amp... on top of that he gave me the correct wire to run from the main panel to be hard-wired into my wh40, so whatever gauge he gave me is correct for either one of 30amp or 40 amp, i can't remember and i don't have it on hand with me ATM and the shops closed.

either way, what would happen if I put in a 30amp circuit and breaker and wired it up to the t104 timer, made for 40amps? and, if he did in fact tell me to put in a 30amp circuit and NOT 40amps, what would the reason for this be?

i have no reason not to run 40amps . as far as i know it just allows me greater expansion room as long as i keep in mind the total draw of the house.

i'll get this all sorted tomorrow when the shops open but id personally just like to know , as im trying to learn as much as i can. i have a feeling i just messed up and im really supposed to run 40amps and i just got the wrong breaker by mistake.

thanks

 

[sparkjumper]

The timer is rated for 40A max,that doesnt mean you need to feed it with 8 wire for a 40A circuit or even 10 wire for a 30A circuit,it's just a maximum rating for the device.The branch circuit wiresize should determine your breaker size.If you are feeding the timer with #10AWG then a 2 pole 30 is what you want.You can undersize a breaker but you cant oversize.You can put a 2 pole 20 on a 10 wire circuit but you cant put a 2 pole 30 on a 12 wire circuit if that makes any sense.Basically you want 30A for 10 wire 20A for 12 wire and 15A for 14 wire

 

[apartmentblower]

The timer is rated for 40A max,that doesnt mean you need to feed it with 8 wire for a 40A circuit or even 10 wire for a 30A circuit,it's just a maximum rating for the device.The branch circuit wiresize should determine your breaker size.If you are feeding the timer with #10AWG then a 2 pole 30 is what you want.You can undersize a breaker but you cant oversize.You can put a 2 pole 20 on a 10 wire circuit but you cant put a 2 pole 30 on a 12 wire circuit if that makes any sense.Basically you want 30A for 10 wire 20A for 12 wire and 15A for 14 wire

ok cool, so i have to make sure i have a have a big enough wire from the breaker feeding my timer to handle either 30 or 40 amp loads. im gonna get a 40 amp breaker and make sure i have the correct #8 wiring. if im doing it already i see no reason why i shouldnt just go for 40


thanks

 

[sparkjumper]

Unless you are doing a huge grow bro that really is overkill.You say you are only pulling 10 amps plus a few fans?240V fans?Anyway 10 wire on a 30A breaker would give you plent of room for expansion as you can safely go 24 amps on a 10 wire 30A circuit.You dont want to mess with 8 wire bro unless the load demands it

 

[apartmentblower]

Unless you are doing a huge grow bro that really is overkill.You say you are only pulling 10 amps plus a few fans?240V fans?Anyway 10 wire on a 30A breaker would give you plent of room for expansion as you can safely go 24 amps on a 10 wire 30A circuit.You dont want to mess with 8 wire bro unless the load demands it

alright man, thats the feeling i got. the 8 wire is hella thick and i think ill have serious problems getting it hardwired into the box. im running 3- 120v fans but they are being run on the same circuit / timer on the 120v receptacles. and then an A/C for summer on its own 120v circuit. so thats under 24 amps. thanks for the info i guess its back to the store for a 30 amp breaker.