How Long For Tow Cables?

The umbilical cord should be long enough that it has no stress placed on it in sharp turns, but shouldn't have excess slack. It should be routed such that it won't be harmed by any pinch points. I like to tie my umbilical to the tow bar near the hinge point. That way the cable length is nearly the same at any angle.

Regarding safety cables/chains - the above regarding the umbilical cord applies to the length of the cables. Do the same with the cables as the umbilical - tie it to the towbar near the hinge point, and cross the cables - left on toad to right attachment point on the two vehicle, etc. Regarding the strength - you must meet or exceed the toad's weight, so 6K is perfect for your 4.5K toad.

The important part is the length of the break-away cable - it must be shorter than the safety cables - if the rig breaks away from the MH, then it must pull the break away switch before reaching the end of the cables.

The same applies whether towing a trailer or a vehicle.

Hope that helps!

Personally, I like the breakaway cable adjusted so that it will energize the brakes ONLY in the event of a total separation of the vehicle from the coach. I do not want the abrupt stress of the fully braked vehicle on the safety cables/chains. IMO, the chance of the cables/chains being yanked far in excess of the rated strength is too great to allow it to happen.
The electrical cable, IMO, should be long enough to avoid being torn loose when turning, but short enough that it will never drag on the ground. Mine is not coiled, so it is taped to the towbar. It works for me.

I can understand your position on the breakaway cable, mowermech! I can imagine that situation, but the idea of a vehicle attached to the motorhome only by the safety cables would be wild too.
Let's say you are moving along at 70, and the towbar gives way but is still attached by the safety cables. Now, you have 1.5 - 3 tons of vehicle flailing around back there, and how do you stop this parade? If the toad is in fully braked mode, at least it won't be crashing into the back of the tow vehicle as you attempt to come to a stop.
There's going to be a lot of damage, either way.

According to my Demco Stay-in-Play instructions:

Step 13: The Breakaway Cable
Clip the breakaway cable to the hitch-receiver tow-cable holes on the coach and clip the lanyard to the loop on the breakaway plug. The length of the cable should be long enough that it will not pull out on the tightest possible turns made in either direction. Also route the cable so that it will not get caught on the tow bar. It should be short enough that it will pull out before the towed reaches the end of the safety cables.

The breakaway cable issue has been cussed and discussed ever since it was invented (which wasn't all that long ago!) There are those who (like me) don't want that braking system activated unless/until the towed vehicle is completely disconnected from the towing vehicle, because we do not believe the "safety" cables or chains are strong enough to hold the shock of a braking vehicle, and we don't want that vehicle suddenly stopping in the midst of rush hour traffic!
Then there are those who believe that the cables or chains are quite obviously strong enough to handle whatever abuse is handed to them. Also, of course, the attaching points are strong enough to handle anything, as well. The idea of their vehicle suddenly coming to a stop in heavy traffic when the cables/chains/attaching points fail is not a worry.
We all have choices.

That is complicated (the concept of the breakaway activating before the end of the safety cables) but I can see it's very important. Blue Ox provided me both: the safety cables and the breakaway cable (lanyard?). Is it likely that they designed them with the correct lengths to work in the way described? I won't assume that, I will check it, but I hope they designed it that way.

Agreed! No matter how our setups are configured, let's hope we never have to test the theories.

Safe travels!