A built-in or a portable spa: load, drainage and electrical requirements

The word "portable" does enormous damage in this subject. It suggests an appliance: it arrives on a lorry, you put it on the terrace, you plug it in. And what arrives on that lorry is a good two tonnes concentrated on four square metres, with water at forty degrees and an electrical supply inside it, which is the worst combination of hazards in the house.

The choice between a built-in spa and a portable one is almost always made on price, and almost always made before looking at the three things that really decide it: the load, the drainage and the electrical installation. This article is about those three.

This is not a point of vocabulary. It means that your spa is inside the regime, with its duties on twin drains, safety devices, water quality and turnover. Anyone telling you that "all that is for pools" is working from the previous rules.

First: the load, and the arithmetic is in plain sight

This is what surprises people most and the easiest thing to check, so here is the whole calculation so that you can redo it with the figures for your own unit. Take an ordinary portable spa, 2.00 × 2.00 m, with a capacity of 1,500 litres and six seats:

Now the comparison, which is what matters. The minimum design live load NSR-10 requires for the private rooms of a dwelling is 1.8 kN/m² (180 kgf/m²). A "portable" spa puts on more than three times that. And it also exceeds the 5.00 kN/m² the code requires for a terrace authorised as a communal recreational element, which is the highest terrace load in the table.

Hence the practical rule. On a ground-bearing slab — a ground-floor terrace, a yard — the problem hardly ever exists. On an upper floor or a roof, it always exists and has to be settled before buying anything: a structural assessment signed by a civil engineer is needed, exactly as for a pool. All of that is in a pool on a terrace, and it applies just the same even if the unit comes on castors.

Second: the drainage nobody plans for

A pool is emptied every few years. A spa is emptied completely every few months, and that is a difference of kind, not of degree.

The reason lies in the arithmetic of the water. Four people get into a pool of 48,000 litres and the proportion is irrelevant. The same four get into a spa of 1,500 litres: the bather load per litre is two orders of magnitude greater, and on top of that the water is at forty degrees, which is the temperature at which everything thrives. Chlorine is used up very fast, dissolved solids build up that no filter removes, and a point comes when the only answer is to change the water.

That means three things have to be planned for that rarely appear on any drawing:

1. 1A drainage point with real capacity. Fifteen hundred litres in one go do not go down a balcony’s rainwater pipe, and they certainly do not go on the garden: Resolución 929 classes pool water as a non-domestic discharge, because it carries chlorine and pH correctors, and refers its management to environmental legislation.
2. 2A filling point nearby. Refilling fifteen hundred litres with a garden hose run across the living room is what makes people stretch the water change well past when it was due.
3. 3Access for maintenance. A portable spa keeps its equipment behind a removable side panel. If you have built it in against two walls and a parapet, that panel does not come off, and the repair begins by moving the unit full.

Third: the electrics, which is where the deaths are

This is the long section, and it is long for a reason the code itself puts better than I could:

RETIE starts from a table worth looking at before anything else: what voltage is safe depending on the state of the skin.

From which follows, and not from any whim, the lighting requirement: lighting inside the shell must be fed from an isolating transformer with an unearthed secondary, a voltage no higher than 12 V, an earthed electrostatic screen between the windings, certified for that use, and a primary at 150 V or less. The alternative the code allows is a luminaire of up to 150 V fed directly from a circuit protected by a residual-current device.

The three metres for a spa

Here is a figure that gets cited wrongly all the time, because the distance for a spa is not the same as for a pool:

Note the last five words, because they close a gap through which half an installation used to slip: including socket outlets rated at 30 A. A spa does not run on fifteen amps; its heater calls for a higher-rated circuit, and until this wording it was arguable whether the residual-current requirement reached it. It no longer is.

The milliamps nobody sets

And here is the absence that has to be declared, because it cuts against almost everything written on the subject.

No Colombian primary source sets a sensitivity in milliamps for the residual-current protection of a pool or a spa. I searched the RETIE in force and the NTC 2050 definition: what exists is a requirement for residual-current protection of "high sensitivity" in damp and wet locations, and a graphical criterion — a curve — instead of a number.

The 30 mA quoted everywhere is in RETIE, but somewhere else: in the chapter on electric vehicle charging points. Attributing it to pools is an extrapolation, not a citation. And it is an uncomfortable extrapolation, because RETIE itself publishes this table:

What else the code requires

And some good news for anyone buying portable. NTC 2050 expressly allows a prefabricated assembly to carry its own factory-fitted ground-fault interrupter, instead of requiring one in the installation, on one condition: that the unit is certified and labelled stating that the device protects all the electrical equipment — pumps, blowers, heaters, lights, controls, wiring. Without that label, the residual-current device goes on the outlet feeding it.

Temperature, and how long you stay in

Resolución 929 sets the maximum water temperature at 40 °C, and adds for similar structures operating at that temperature three duties that did not exist before: a timer set to a maximum of fifteen minutes, a start button at least five metres from the structure, and signage warning vulnerable groups of the risks, stating as well the maximum time bathers should remain in it.

For covered enclosures the resolution adds air parameters that are rarely met: CO₂ between 400 and 600 ppm, relative humidity of 50% to 70%, air temperature between one and three degrees above that of the water, air changes of four to six times the volume of the space per hour and a minimum of 8 m³ of air per bather, with a thermohygrometer and a CO₂ meter on view.

Entrapment: the risk is greater, not smaller

There is an idea that a spa, being small, is safer than a pool. On suction it is the other way round, for three reasons that compound: the bather is seated, often directly over the suction outlet; the volume is small, so the pump moves a great deal of flow relative to the water present; and loose long hair floats at seat height.

The rules apply the same things as to a pool, and now beyond argument because a spa is a similar structure: two or more hydraulically balanced submerged drains, at the deepest part, at least 0.90 m apart, with an anti-entrapment cover, a vacuum release system and an emergency stop button. And the cover must be at least four times the area of the discharge pipe, in order to minimise suction currents.

And what I set out in Ley 1209: what it really requires still stands: the technical regulation that was to define the performance of these devices was never issued, and Resolución 929 still writes it in the future tense, referring meanwhile to the supplier’s own declaration of conformity. "Type-approved", today, still means the manufacturer signed a piece of paper.

The water: half an hour, not six

Resolución 929 sets the turnover time by type of tank, and gives similar structures 0.5 hours, with twelve turnovers a day. A restricted-use pool gets between four and six hours.

Half an hour against four or six. That single number explains why a spa is not hung off a pool’s machinery, which is the subject of a pool and a spa together. It also explains why the electricity consumption of a spa comes as a surprise: its recirculation pump works six hours a day on a tiny volume, and the heater holds forty degrees for all twenty-four.

As for water quality, the parameter most often breached in spas is the microbiological one. Health legislation requires the absence of Pseudomonas aeruginosa, the bacterium responsible for hot tub folliculitis, and precisely the one that thrives in warm water with little chlorine and plenty of biofilm in the jet pipework. A spa that smells odd does not need more chlorine: it needs a water change and its lines cleaned.

Built-in or portable: the full comparison

The conclusion I draw from having seen both fail: the portable one is not the cheap option, it is the quick option. What it saves is builder’s work and time; what it does not save is the structural assessment if it goes on an upper floor, nor a compliant electrical installation, nor the drainage point. When a quotation for a portable spa comes in very cheap, it is almost always because those three are not in it.

What has to be settled before buying

1. 1The filled weight of the unit, from the manufacturer’s data sheet, plus the bathers, divided by its footprint. Compare it with what the slab will take.
2. 2If it goes on an upper floor or a roof, the structural assessment signed by a civil engineer. Before buying, not after.
3. 3The drainage point, with capacity for a complete emptying and a lawful destination.
4. 4The electrical circuit: dedicated, with high-sensitivity residual-current protection, and with the isolator in sight and at least 1.5 m away.
5. 5The equipotential bonding of the metal parts and of the perimeter surface, in 8 AWG copper or larger.
6. 6The two drains 0.90 m apart with their covers, their vacuum release and their stop button.
7. 7If it is a community of owners, authorisation from the general meeting: the slab is common property even where the terrace is for exclusive use.

None of the seven is expensive if settled beforehand. All seven are expensive afterwards, and two of them — the structure and the drainage — may have no solution at all in the place chosen, which is exactly what it is worth finding out while the spa is still in the shop.