Climatic ratings U1 and UHL

Author: Viacheslav Yurdyk, Quality Engineer at LK Energy Group.
Acceptance of equipment at the plant (quality control department) and technical supervision on electrical installation sites.

Short answer

«U1» and «UHL2» are climatic version designations under GOST 15150-69 (no longer in force in Ukraine): the first part denotes the climatic region, the digit denotes the placement category. U1 is a product for a temperate climate operating in the open air; UHL is a temperate-cold climate.

The main thing to know today: GOST 15150-69 itself is no longer in force in Ukraine. No direct replacement for these letter designations has appeared: the European standards in force, the DSTU EN/IEC 60721 series, classify environmental conditions, rather than issuing a «U1» designation. So the designation has remained the working language of the industry — it appears in product documentation, in designs and in questionnaires — but the contract must rest on figures, not on a letter: temperature range, degree of protection, humidity, altitude above sea level.

And one more thing worth knowing: PUE:2026 (PUE — the Ukrainian electrical installation code) does not reference GOST 15150 at all. It requires that the climatic version match the environmental conditions [п. 4.1.37] — that is, it shifts the question from the language of designations to the language of actual conditions.

What the letters and digits mean

The first part is the climatic region:

Designation	For which climate
U	temperate
UHL	temperate-cold
HL	cold
T	tropical
M	marine (temperate-cold)
O	all-climate version (all land regions)

The digit is the placement category:

Category	Where the product is installed
1	in the open air
2	under a canopy or in a room where conditions are close to outdoor
3	in an enclosed room without artificial climate control
4	in a room with artificial climate control (heating, ventilation)
5	in rooms with elevated humidity (basements, tunnels)

So U1 is a product for a temperate climate designed to work in the open air; UHL4 is for a temperate-cold climate, but in a heated room.

🔑 The most common mistake in reading the designation. The letters and the digit together give two different characteristics, and «better» on one does not mean «better» on the other. UHL4 is not «stronger» than U1: it is designed for a colder climate, but only for indoor use. UHL4 must not be installed in the open air, even though the letter looks «more serious».

The status of this standard in Ukraine

GOST 15150-69 is no longer in force in Ukraine. The withdrawal took a long time: the deadline was postponed several times by orders of the standardisation body, which is why different sources give different dates. We deliberately do not name one specific date — what matters is not the year but the current status of the document.

The only exception, left in place by a separate decision: this GOST may be applied solely for the manufacture and/or supply of products ordered by state customers for the construction of structures (Order No. 148 of DP «UkrNDNTs» dated 24.06.2026).

What replaced it — the honest answer: there is no direct replacement for the designation. Ukraine applies the adopted European standards of the series DSTU EN / DSTU EN IEC 60721 «Classification of environmental conditions» (adopted in 2022, several parts). But they are built differently: they classify the conditions themselves — temperature, humidity, vibration, the installation environment — and assign them their own classes. They do not issue designations of the «U1» type.

This has created a situation worth understanding correctly:

the U1/UHL2 designations have not gone anywhere — they appear in product documentation, in designs, in questionnaires and in engineers' language. This is neither a violation nor deception;
but a reference to a withdrawn document is no longer an argument in a dispute. If the parties disagree on the conditions a product is designed for, the matter will be settled by the figures in the data sheet, not by a letter.

What the PUE requires instead

The 2026 Rules do not reference GOST 15150 even once. Instead of a designation they require compliance with actual conditions — and they do so in two places.

For outdoor switchgear [п. 4.1.37]: - the climatic version of the switchgear must match the conditions of the natural environment; - the switchgear must have an appropriate degree of protection against contact with live parts and ingress of solid foreign objects and liquids; - within the switchgear it is necessary to maintain the temperature regime for the installed equipment in accordance with the manufacturer's requirements.

For connected devices and apparatus [п. 3.4.6]: the climatic version must match the environmental conditions and safety requirements.

🔑 What this changes in practice. Previously you could write «U1» in a specification and consider the question closed. Now the correct approach is different: state the conditions — minimum and maximum temperature, humidity, dust levels, whether there is direct sun and precipitation — and check that the product is rated for them. The designation remains a convenient shorthand, not a proof.

Why this is not a formality: an example from a measurement

In our data sheets the climatic version U1 means, among other things, an upper operating ambient air temperature of +40 °C. This is not an abstraction but the limit beyond which the manufacturer guarantees nothing.

At one site, in the transformer chamber, a pyrometer registered up to 88 °C on the surface of the equipment. The cause was not the equipment: forced ventilation had been removed from the substation — there was nothing to power it from. In other words, the thermal regime in the room no longer matched what the product was designed for, and this directly violates the requirement of clause 4.1.37: within switchgear the temperature regime for installed equipment must be maintained in accordance with the manufacturer's requirements.

🔴 Why this figure must not be placed next to «+40 °C». A pyrometer measures the surface, whereas +40 °C in version U1 is the upper operating temperature of the ambient air. These are different quantities, and one does not follow from the other: a surface can be hot from the equipment's own losses. Therefore 88 °C on the surface does not prove that the air in the chamber exceeded +40 °C — it proves something else: that the thermal regime in the room is wrong and must be measured properly.

What follows from this in practice. A climatic version is verified not with a pyrometer through the door but by the conditions of the room: air temperature, ventilation, heat dissipation of the equipment. A pyrometer shows that a problem exists; it cannot prove compliance or non-compliance with the conditions of use.

The conclusion for the client is simple. A climatic version is not a tick-box line in a specification. It is the declared set of conditions under which the product performs as promised. If the actual conditions on site are different, neither the letter in the data sheet nor a certificate will help.

How to word the requirements in a questionnaire

Instead of «version U1» — or in addition to it — state:

where it stands: in the open air, under a canopy, in an unheated or a heated room;
the temperature range of the ambient air, realistic for your site;
the degree of protection (IP) — against dust and water;
humidity and whether condensation occurs;
special conditions: aggressive environment, salt mist, dust, vibration, altitude above sea level;
whether heating or ventilation is required for the compartments — and what they will be powered from.

The last item is usually remembered last, and it pulls an auxiliary distribution board along with it.

Frequently asked questions

What does U1 in an equipment name mean?

It is the climatic version under GOST 15150-69 (no longer in force in Ukraine): «U» is a temperate climate, «1» is the placement category «in the open air». That is, the product is rated to work outdoors in a temperate climate.

How does U1 differ from UHL1?

By climatic region: U is a temperate climate, UHL is temperate-cold, that is with a lower minimum operating temperature. The placement category is the same in both cases — in the open air.

Is UHL4 better than U1?

No, it is simply different. UHL4 is rated for a colder climate, but only for a room with artificial climate control. It must not be installed in the open air, despite the «more serious» letter. Comparing designations as «better/worse» is incorrect: they describe two different characteristics at once.

What do the digits from 1 to 5 mean?

The placement category: 1 — in the open air; 2 — under a canopy or in a room with conditions close to outdoor; 3 — in an enclosed room without climate control; 4 — in a room with artificial climate control; 5 — in rooms with elevated humidity.

Is GOST 15150 still in force in Ukraine?

No, the document is no longer in force. It was withdrawn in stages and the deadline was postponed several times — hence the different dates in different sources. What matters in practice is different: today it is a document no longer in force, and it cannot be cited as a valid standard.

Why is the U1 designation still written everywhere?

Because no direct replacement for the letter designation has appeared, and the language of the industry changes more slowly than the list of standards. The designation remains a convenient shorthand in product documentation, in questionnaires and in designs. It is not a violation — but neither is it an argument in a dispute: proof has to come from the figures in the data sheet.

What replaced GOST 15150 in Ukraine?

Not by a single document and not «one for one». The adopted European standards in force are the series DSTU EN / DSTU EN IEC 60721 «Classification of environmental conditions» (adopted in 2022). They classify the conditions themselves — temperature, humidity, vibration, the installation environment — and assign them their own classes rather than a designation of the «U1» type.

May GOST 15150 still be applied?

There is a narrow exception: application is permitted solely for the manufacture and/or supply of products ordered by state customers for the construction of structures (Order No. 148 of DP «UkrNDNTs» dated 24.06.2026). For all other cases the document is no longer in force.

What does the PUE require instead of a designation?

PUE:2026 does not reference GOST 15150. It requires that the climatic version match the conditions of the natural environment, that the installation have an appropriate degree of protection and that it maintain the temperature regime required by the manufacturer [п. 4.1.37]. For connected devices and apparatus — the same plus safety requirements [п. 3.4.6].

How should the requirement for equipment be worded then?

State the conditions, not the letter: where the product stands, the real temperature range on site, the required IP degree of protection, humidity and the presence of condensation, special conditions (aggressive environment, dust, vibration, altitude), and whether heating and ventilation are required. The designation may stay as a shorthand — but the requirement must be in figures.

What happens if the actual conditions are worse than the product's version?

Formally the equipment remains serviceable and certified; in fact it operates outside its conditions of use, and the manufacturer's warranty does not cover such a regime. The Rules require maintaining the temperature regime required by the manufacturer [п. 4.1.37], so in such a case the question is not about the cabinet but about the ventilation of the room. Our case: forced ventilation was removed from the transformer chamber, there was nothing to power it from — and the thermal regime no longer matched the design.

Are the climatic version and the IP degree of protection the same thing?

No. The climatic version describes the climate and the place of installation (temperature, humidity, region), IP describes the protection of the enclosure against ingress of solid objects and water. Both are needed and neither replaces the other: a product can be U1 with different IP ratings.

We will select the version to suit your site conditions

The climatic version and the degree of protection are selected for the place of installation, not «to have more of it». Send us a single-line diagram or a completed questionnaire and we will tell you which version you actually need and what it changes in the price.

This material is provided for information only and is neither an offer nor legal advice. We do not publish the full text of the Rules — only quotations with clause numbers; obtain the official text from the source indicated above.

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Climatic ratings U1 and UHL: what these letters mean