THE ACTUAL CODE REGARDING CABLE SPACING IS NOT CLEAR.
CODE SAYS:
There is nothing specific regarding cable spacing in building code, so consumers must take all factors into consideration and meet the code requirements for standard building materials.
CABLE RAILING DIY SAYS:
Building code requirement is the same as any railing and states that a balustrade (in this case cable) cannot be greater than 4 inches and as a test a railing balustrade (cable) cannot allow a 4-inch sphere to penetrate between cables with reasonably applied force. Given the ability for cable to deflect (move) when pressure is applied, the practical application of cable railing to meet code requires spacing much tighter than 4 inches. Safe spacing for cable railing is an absolute maximum of 3 inches between cables if posts are not more than 4 feet apart. Many products space cables, posts and stabilizers even closer. If faced with a situation where even cable spacing will end up over or under 3 inch spacing, never go over. Closer is better and safety should be your priority.
CODE COMPLIANCE:
Cable will generally deflect up to 25% under reasonable pressure (emulating handling by occupant) if post spacing is 4 feet or less. This is where we derive our recommendation for cable to be spaced no more than 3 inches apart and 4 feet between posts. A 25% deflection will create a space of 3.75 inches under reasonable pressure. Never space cable more than 3 inches.
POST SPACING WITH HORIZONTAL CABLE FOR CODE COMPLIANCE?
CODE SAYS:
Again there is no specific code for cable railing post spacing, but you must comply with the general code for railings. The recommendation is to space posts no more than 4 feet apart or use an intermediate stabilizing device to maintain allowable deflection. Inspectors will often be required to make their own judgment regarding compliance factors and will rarely be forgiving if you bend the rules.
CABLE RAILING DIY SAYS:
Never space posts more than 4 feet without an intermediate stabilizing device (cable stabilizers). We call these supports cable stabilizers as this is their only job. They are not considered a post or structural support. Cable stabilizers are generally 1” x 1” or 1” round tubes with pre-drilled holes.
BEST PRATICES:
Discuss your cable railing design with your local code officer before finalizing design or installing. We see several occasions where code enforcement officers have reasonable additional requirements.
Always follow manufacturer specifications and instructions, but if you need to adapt to any situation, always err on the side of safety.