SW6DE hot cables

Many people and possibly some RV manufacturers install a household type light switch (known as a "snap switch" on the inside so that you leave the switch on the water heater on, and then switch it on and off with the switch inside. This is for the 120v AC heating element.

Some installations may, as noted above, use a 12v DC controlled relay to switch the 120v AC.

Clearly something is building up a lot of resistance in the circuit and causing the overheating of the wire, etc. Personally, I would replace every bit of the wire (electrical Non Metallic Cable, aka "Romex™") from the distribution panel to the water heater, any 120v AC swtiches on the inside with top quality 20 amp "motor rated' switches (they have much heavier contacts than ordinary switches) and also the switch installed in the water heater and the element.

This may sound radical, but is a fairly inexpensive proposition so far as parts go, and any good electrical savvy person could handle this easily.

Charles

If you are still having trouble, call me and I can help you over the phone.

Suburban SW6DE does NOT use a 'relay' unless RV MFG installed/Modified water heater controls

AC from Circuit Breaker goes to AC Junction Box (left side of WH Tank looking from rear)
From Junction Box to OEM on/off switch in outside compartment then UP to the 120VAC Set of t-stats (left side) then down to element
Black wires....120VAC Hot
White Wires....120VAC Neutral

Check the wire connections in the AC Junction Box...they are connected using Wire Nuts (not the best for staying tight bouncing/vibrating down the roads)
Loose connections.....high resistance===HEAT


OEM element is 1440W 120VAC element....12amps

ktmrfs wrote:
most remote hwh switches are 12V running to a relay that switches the 120V to the element. If it really is 120V to the switch it should be #12 romex wire and a UL listed wall switch or toggle rated for 120V and at least 15A.
….
here is a link to a typical suburban wiring diagram. Note NONE of the switches are 120V, they are ALL 12V.

The black switch on the front bottom left corner of a Suburban water heater is 120 VAC. If there is a switch inside the RV for operating the WH on electric it is a 12 VDC switch that activates an interposing relay to send 120 VAC to the switch on the water heater.

Look at figures 5b and 6b if there is an inside switch for operation on electric. The relay coil is shown in 5b. The relay contact and 120 VAC switch are shown in figure 6b.

Look at 5a and 6a if it does not have an inside switch for electric.

Suburban manual.

most remote hwh switches are 12V running to a relay that switches the 120V to the element. If it really is 120V to the switch it should be #12 romex wire and a UL listed wall switch or toggle rated for 120V and at least 15A.

I haven't checked my suburban but i think the switch on the WH is also 12V switching a relay for the 120V.

BTW a friend had a brand new motor home where they had wired the switch to 120V rather than 12V and on walk through water heater was full, switched on the electric element and pretty quick smoke came rolling out. NOT a good thing.

here is a link to a typical suburban wiring diagram. Note NONE of the switches are 120V, they are ALL 12V.

https://answers.rvupgradestore.com/3519769/DO-YOU-HAVE-A-WIRING-DIAGRAM

Need to add to look closely at the switch for it's rating.
Look at the element for it's rating.
Someone may have changed to higher wattage.
Divide wattage by 120 to get amperage. Switch should be rated at least 125 per cent of calculated amperage.

Make and year of rig
Normally the switch for the 120 volts is control only. Control operates a relay.
your model does not.
Manual