Introduction: 3 - 4 Wire 240v Multi Ballast Grow Timer

how to change a 3 wire 240v system into a 4 wire 240v system

Step 1: Getting to Know Your Box

the first thing you will need to do is get familiar with your specific power box. Not all timer boxes are made the same... some use internal timers, others use relays to switch on the 240v power... the latter is what we will be working with in this instance... Either way they are the same basic idea.

The idea is that building codes have changed and if you own an older 3 prong power box you will be unable to plug it into your updated wall socket.

Step 2: Basics in A.c. Power

First things first...This project can be extremely dangerous if done incorrectly... Always make sure you use the correctly rated wire... DO NOT use old or damaged wire! DO NOT plug this unit into the wall until you have triple checked everything. Turn off all breakers to every room before plugging the modified unit in the first time. DO NOT. plug in your ballasts until you are sure the unit is working correctly! YOU ARE PLAYING WITH POTENTIALLY DEADLY AMOUNTS OF ELECTRICITY!
To modify this you will need to have a basic knowledge in a.c. power. There are 4 parts to this type of power setup... you have 2 powered leads. These are called "hot 1" and "hot 2". Each of these carry a 120v a.c. current. Be careful with these! You also have a common and a ground. In the older 3 prong system the common and ground were passed through the same wire... this is no longer the way buildings are wired. These days the common and ground are passed through separate cables. The standard wiring color code goes as follows.

Green = Ground
White = Common
Red = Hot
Black = Hot

if your cables aren't labeled then bust out your multimeter and check which lead goes where... and remember "round is ground" meaning the round socket pin will be the ground...

Step 3: Disassembly

1: remove fastening attachments...
2: find and remove ground attachment
3: find and remove the hot leads attached to the relay
4: remove cable from the case

Step 4: Building the Plug

this is an optional step... if you buy a 4 prong pre build dryer cable you can skip this step. I built my own because I wanted a longer cable. Its your choice.

1: Strip the outer insulation and cut the wires to the appropriate lengths

2: wire the leads into the appropriate pins... White into the L shaped pin, Green into the Round one, and Red and Black into the flat pins

3: insert the pins into the housing... double check that no strands of wire are loose or touching... close down the enclosure and lock the cable in place

Step 5: Wiring the Box

1: measure and strip the other end of your cable for the proper length of wire for your specific needs

2: don't leave excess wire floating around in the box... cut off your excess

3: re-wire the green and white wires into the same place you removed the ground from...

4: prep the red and black cables

5: use appropriate mounting hardware to fasten the hot leads... you really don't want these getting loose!

6: attach the hot leads to the relays where you took off the original leads

7: tension clamp and double check all of the wiring before you close up the box

Step 6: Final Safety Precautions

This is just a safety precaution but an extremely important step! In case you did somehow wire something wrong you do not want to be near the box or plug when power is initially turned on. This can create fires and can be potentially fatal if wired wrong!
Turn off all breakers to every room before you plug this in the first time. Now with all breakers in your unit turned off you are ready for your first test... plug in the 240 and go to your breaker box and flip only your 240 breaker. If you connected everything correctly nothing will happen... if something is wrong you will know. there will be huge sparks and possibly an electrical fire... just don't wire it wrong and you will be fine!

after you have tested this for a while and nothing is heating up or giving off an electrical fire smell you are ready to turn the power back to everything and plug in your ballasts!

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tomatoskins made it! (author)2015-10-08

Super helpful for switching from 3 to 4 wire systems!