Basic knowledge for explosion proof of electrical equipment

explosion proof
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I will explain the explosion proof structure of electrical equipment .

A challenge faced by anyone who handles equipment at a chemical plant . One of them is explosion proof.

I want to automate this!

Impossible because it is non-explosion proof!

This kind of exchange will not happen once or twice.

  • It can’t be helped because there is no explosion proof
  • Explosion-proof is required, so it can’t be helped that it takes time and delivery

That is certainly the case.

There is a tendency to focus only on the issue of explosion-proof regulations, and there are surprisingly few people who understand the technical content in the first place.

Therefore, we have summarized the knowledge of explosion protection that mechanical engineers should know.

three elements of combustion

Explosion-proof construction refers to the construction of electric motors, etc., against explosions.

Parts that handle electricity, such as electric motors, may explode if they come into contact with combustible gas.

As a condition for a fire explosion to occur

  • ignition source
  • Combustible material
  • Combustion support

There are three points. These are called the three elements of combustion .

A realistic countermeasure is the ignition source .

Combustibles and combustibles cannot be removed during chemical plant operation.

  • Combustibles are combustible gases in the surroundings.
  • The combustion support is oxygen.

In terms of motors, the spark that is the ignition source is a problem.

Explosion-proof structure is the structure for this.

Types of explosion proof

There are many types of explosion protection.

Increased safety explosion proof and explosion proof

Explosion-proofing and increased safety are important for explosion-proofing of electrical equipment used in chemical plants .

  • A structure that does not ignite the external gas even if an explosion occurs inside the pressure-resistant   explosion-proof
  • Increased safety, explosion-proof structure that increases the degree of safety and prevents it from becoming a source of ignition

This is a qualitative expression. A little more concretely,

  • Explosion proof is electric circuit is general and external to mechanical. It is made strong.
  • Increased safety explosion – mechanical strength. In addition to an increase in electric circuit. We must also improve the nature of

can be expressed as

In general, flameproof is said to be of higher rank.

However, neither pressure-resistant explosion – proofing nor increased safety explosion- proofing satisfy the three measures against ignition sources, combustible substances, and combustion-supporting substances at the same time.

Explosion proof is more expensive and takes longer to deliver

Pressure-resistant explosion-proof is higher than safety-enhanced explosion-proof, and it is said that the delivery time is long.

This is probably the reason why flameproof is often said to have a higher rank.

Production of explosion proof for increased safety is on the decline

However, some companies have discontinued the production of safety-increased explosion-proof products.

I have a feeling that the flow will increase from now on.

I’m not a motor manufacturer, so I don’t know.

From 2021 onwards, logistics stagnation due to the corona crisis has become a social problem. In particular, it must be said that increased safety and explosion-proofing are very strict. It’s a big problem in the supply chain.

Explosion proof

In the internal pressure explosion-proof structure, nitrogen gas is sealed inside the container to increase the pressure.

It is a mechanism that prevents an explosive atmosphere from entering the container.

This is the same concept as the internal pressure chamber .

The concept is almost the same as the pressure-resistant explosion-proof structure, so the electric circuit is common.

The disadvantage is that the installation cost increases due to the introduction of the enclosed gas.

Oil immersion explosion proof

The idea is to put the electric circuit in oil and prevent the intrusion of an explosive atmosphere .

Same as the internal pressure explosion-proof type, it has the advantage of preventing the intrusion of an explosive atmosphere.

  • that the oil is stable
  • No accumulation of combustible gases due to decomposition of oil
  • Oil with low electrical conductivity

Various requirements are required.

In this case, I think the internal pressure explosion proof is simpler.

Intrinsically safe explosion proof

Intrinsically safe explosion-proof is achieved by lowering the current/voltage to operate the electric circuit.

The idea is to prevent fire explosions by preventing electrical sparks and temperature rises .

Measure the electrical spark generated by the electrical device, and if it is less than the minimum ignition energy,

The idea is that it can be used in that explosive atmosphere.

Special explosion proof

Other ideas include powder filling and resin filling.

This is considered as an advanced form of oil-immersed explosion proof.

Structural Standards/Technical Standards

There are two types of explosion proof standards.

Structural standards and technical standards .

Any electrician would know the difference.

But for machine shops, they must have the impression that they don’t really understand . Me too.

I sometimes remembered d2G4 for pressure-resistant explosion-proof, eG3 for increased safety explosion-proof, etc.

Before I knew it, the standard name had changed and I was confused.

Then, I came to the conclusion that it doesn’t matter and I just need to understand whether it’s pressure-resistant explosion-proof or safety-increased explosion -proof.

Structural standards are Japanese standards

Simply put, the structural standards are Japanese standards .

“Electrical Machine Equipment Explosion-proof Structural Standards” (Ministry of Labor, 1969) Notification No. 16

seems to be the standard.

Technical standards are international standards

To put it simply, technical standards are international standards .

“Internationally harmonized explosion-proof guidelines 2015” (August 31, 2015) 0831 No. 2

seems to be the current standard.

d2G4 and eG3 are structural standards

When I started working, I understood that flameproof was d2G4 and increased safety was eG3 .

This is a structural standard .

This name is seldom seen today.

It is now becoming a technical standard .

Difference between structural standards and technical standards

Let’s see the difference between structural standards and technical standards.

Zone 1zone 2
Structural standardIntrinsically safe i
Flameproof d×
Pressure explosion proof f×
Increased safety explosion proof e×
Oil-immersed explosion proof o×
Special explosion proof s
technical standardsIntrinsically safe Ex ia
Intrinsically safe Ex ib×
Flameproof Ex d×
Pressure explosion proof Ex p×
Increased safety Ex e×
Oil-immersed Ex o×
Special explosion proof Ex s

The main difference between structural standards and technical standards is whether or not the increased safety explosion-proof can be used in Class 1 locations .

It can be interpreted that the structural standards are stricter .

The following features are also important.

  • Intrinsically safe is the safest
  • Flameproof and pressurized explosionproof are the second highest safety after intrinsic safety.
  • Increased safety explosion-proofing loses safety due to deterioration failure of parts
  • Safety is compromised due to deterioration and leakage of oil.

Based on these ideas, we determine whether or not the system can be applied to Class 0, Class 1, and Class 2 locations.

The reliability of increased safety explosion- proof is low because

Reliability of electrical parts < Reliability of mechanical parts

That’s why. This trend is particularly strong in Japan.

However, I also have doubts about the reliability of pressure explosion-proof devices.

It is important that the internal pressure is maintained with air or nitrogen, but there is no monitoring index for this.

In this sense, I don’t think it’s much different from increased safety explosion-proof.

explosion class

Explosion classes are basically divided into three stages.

Classify by maximum safe clearance for gas or steam .

The notation is slightly different between the structural standard and the technical standard, and it tends to be complicated.

First, let’s look at the structural standards.

1,2,3 in structural standards

Explosion classes are expressed in three stages: 1, 2, and 3.

explosion classMaximum safe clearance for gas or steam
1Over 0.6mm
2More than 0.4mm and less than 0.6mm
30.4 mm or less

Almost all texts end here.

A layman doesn’t understand this.

The higher the grade number, the stronger and strongerPlease be aware of that.

This way of looking is to look at a specific substance of explosive grade.

Hydrogen and acetylene fall under class 3 .

Most other substances are grade 1.

From this relationship, we can see that grade 3 is more severe.

  • Hydrogen has a wide flammable range
  • Acetylene is flammable

You can organize your grades by linking them with these traits.

The relationship between the above explosion class and gap is

  • The higher the grade , the smaller the clearance.
  • The smaller the gap , the more difficult it is for substances with a high explosion grade (flammable) to pass through.

can be interpreted as

Technical standards are II A, II B, II C

Technical standards are also divided into three levels, the same as structural standards.

The number for clearance is different.

explosion classMaximum safe clearance for gas or steam
II AOver 0.9mm
II BMore than 0.5mm and less than 0.9mm
II C0.5mm or less

The structural standards are on the lower side, so you can see that they are being treated harshly.

Ignition degree/temperature grade

Ignition degree is an expression on the structural standard side.

expressed in 6 stages.

degree of ignition

degree of ignitionignition temperature
G685°C or less

The higher the number, the stronger and stronger

Please be aware of that.

It can be positioned as a standard that can be applied to substances with low ignition temperatures.

temperature class

Temperature grades are expressed in 6 stages of T1, T2, T3, T4, T5, and T6.

This is used in the same sense as firing rate.

The degree of ignition is defined for the ignition temperature, while the temperature class is defined for the maximum surface temperature.

It is related to the ignition temperature, which is a characteristic value of the substance, while the temperature class is related to the maximum surface temperature determined by the structure of the object.

The degree of ignition seems to be correct because it uses the essential eigenvalue, but I think it is more rational to specify it by the surface temperature because the actual ignition is determined by the surface temperature.

d2G4 and eG3

Explosion-proof symbols are divided into structural standards and technical standards, each of which is distinguished by the type of explosion-proof structure.

There are types such as pressure-resistant explosion-proof and increased safety explosion-proof.

Furthermore, they are classified according to the explosion class and degree of ignition.

First, let’s focus on structural standards and see what d2G4 and eG3 mean.

Meaning of d2G4

d2G4 means:

  • Explosion-proof d
  • explosion class 2
  • Ignition degree G4

Combining these is d2G4.

The d in flameproof is just a fitting of the symbols and has no meaning.

Explosion class 2

Explosion proofs are designed with gaps, so there are regulations for explosion classes.

However, there are few types of explosion class 3, and special requirements other than explosion protection may be received, so we will consider it as an exception.

It is thought that 2 is adopted as a general explosion class with the aim of being able to use anything other than explosion class 3.

Ignition degree is G4

Ignition is a very similar idea.

Most substances handled by chemical plants have values ​​lower than G3.

Substances corresponding to flammability G4 are acetaldehyde and ethyl ether.

Is it a substance that is unfamiliar to machine shops?

Acetaldehyde is generally a substance that should be sober. . .

Gasoline and hexane correspond to ignition degree G3.

These are materials that we use on a daily basis.

It seems that G3 may be used as a general ignition degree, but it is thought that G4, which is one rank higher, is adopted as a general ignition degree.

Meaning of eG3

eG3 means:

  • Increased safety explosion-proof e
  • Ignition degree G3

There are no regulations regarding explosion class for increased safety explosion-proof.

This is because the design is not based on the concept of “gap”.

The ignition degree is G3.

As noted in the d2G4 section, most chemicals have G3 or lower values.

That’s probably why G3 was adopted as a general ignition level for increased safety and explosion protection.

In order to make the explosion-proof type more reliable than the explosion-proof type with increased safety, the ignition degree of the pressure-resistant explosion-proof type was raised by one rank to G4.

I can’t say it. These are probably the correct interpretations.

by technical standards

Both d2G4 and eG3 are expressions based on structural standards.

How is it expressed in technical terms?

Structural standardtechnical standards
d2G4Exd IIB T4
eG3Exe II T3

I don’t like the extra symbols in it (laughs).

The symbolic representation itself is much simpler in structural standards.

This is probably because the structural standards were set first.

Technical standards are prefixed with Ex.

I arbitrarily interpret it as Extra. The mechanic shop is a symbol that can be ignored.

d or e after Ex

This is the most important.

The idea of ​​not bringing the most important symbols d and e to the beginning is the opposite.

I think it’s a sign that ignores the site.

That’s why I don’t like technical standards.

Both IIB and II are explosion grades, but they can also be ignored.

The idea of ​​the subsequent standard that an explosion class of 2 is enough is taken over as it is.

T4 and T3 are the same as G4 and G3.

Ex and II were added as extra symbols to the technical standards in addition to the structural standards.

I think it’s enough if you understand.

Memories that can be used on site

There is an opportunity for mechanical engineers to come across explosion proof symbols.

Let’s practice at least here to make it a level that can be used properly.

Confirmation of motor drawing

Mechanical engineers are often in charge of purchasing electric motors together with the equipment itself.

Here, the first to check the drawing is the mechanical engineer

The mechanical engineer is responsible for supervising and checking the entire installation.

It’s about electricity, so I’m sorry if I don’t know.

At the very least, you have to check whether the explosion proof standards meet your requirements.

Therefore, it is necessary to decipher the explosion-proof standard from the motor drawing.

Confirmation during on-site construction

It is necessary to confirm whether the purchased equipment has been properly constructed at the site construction.

This is where you need the ability to decipher the motor nameplate.

Explosion proof is d, increased safety is e

At the field level, only flameproof and increased safety are used.

These two symbols are d for flameproof and e for increased safety.

It’s OK if you can use this at the reflection level.

Let me give you a personal reminder.

e is easy/cheap/safe

It’s a sudden forcible rhyming and a forcible twist.

Even in studying for entrance exams, I have only done a little bit of this kind of scrutiny.

I never thought that I would have to do such a thing after joining the company.

e is e for easy.

I cannot give this up.

Many symbols for increased safety explosion-proof are eG3, and eG has the same reading as easy, so this is easy to associate.

From the next point onwards, it’s super forcible.

cheap because it’s easy

It is an association that it will be cheap because it is easy and simple.

Cheap and safe are both cheap

The last is forcing.

Both cheap and safe have the word “cheap” in them.

I have this pathetic way of remembering.

easy → cheap → safe (explosion proof)

d is before e

d is alphabetically before e.

Don’t you have an image that the one in front looks stronger?

Explosion-proofing seems to be stronger than explosion-proofing with increased safety, right?

Therefore, I understand that d, which seems to be stronger than explosion-proof for increased safety, is stronger than e . This is too farfetched.

d is before e



Basic knowledge of explosion-proof electrical equipment was explained.

Explosion-proof type・Structural standards and technical standards・Explosion class・Ignition degree・Temperature class

The words d2G4 and eG3 are immediately associated with explosion proof, but I would like to understand the system.

Please feel free to post your worries, questions, and questions about the design, maintenance, and operation of chemical plants in the comments section. (Comments are at the bottom of this article.)

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